November 2017

Ultra light caravans and fifth wheelers are rare, but feasible. Here’s how it is be done using hi-tech materials. One, over 9 metres, was under 2000 kg.

Australia’s Glenn Portch has spent the past 20 years experimenting and building ultra caravans. His own 11.3 metre unit weighs 3200 kg. Its payload is 1200 kg. The last of the eight he made is 9.1 metres, and originally under 2000 kg.

Glenn’s ultra light caravan research lacks financial motive. He retained one (shown below) for himself. The others were sold at close to cost price. In so doing he has shown what is possible in ultra light caravan design.

Glenn Navigator web

Glenn’s own ultra light Navigator is 11.3 metres. It weighs 3200 kg and its carrying capacity is 1200 kg. Pic: Glenn Portch

Glenn’s first engineering was in the 1980s. He sought a pair of up-market loudspeakers. Most, however, were costly, available only in black, and lacking styling. He researched extensively. Then, using best available components, designed and built them himself. They had gloss white enclosures with black granite overlays. A Sydney hi-fi shop owner (that I also knew) asked if he could build more.

Glenn and his (then) partner set out to build the world’s best. Within a few years they exported the (Audio Definition) loudspeakers to nine countries. They had 14 local dealers. The products were not cheap. Their sound quality necessitated top quality components. The superb cabinet finish demanded years of research and testing. They made lower-priced models too, but the top ones were $35,000 a pair. They were so successful they won many top world awards.

Ultra light caravans – fifth wheel format

Glenn later became interested in travelling around Australia. Often in the USA – researching audio, he could see fifth wheeler caravans rapidly gaining acceptance. The fifth wheeler configuration (and inherent stability) appeals to his knowledge of the physics involved. But whilst liking the concept, those available seemed unnecessarily heavy. Some absurdly so. So, once again Glenn decided to build his own. But ultra lightly!

Ultra light caravans – strength

Despite aluminium-framed aircraft since 1900, many caravan builders assume weight confers strength. Many a locally-made caravan’s floor and fit-out uses heavy plywood. This adds little structural strength, yet considerable (unnecessary) weight. Such weight necessitates a heavier chassis, suspension and tyres to carry it. As a result, many US and Australian-built caravans are heavy, yet not necessarily strong.

A few local makers use lightweight body construction. Most, however, retain a heavy (yet not strong) chassis, still, and unnecessarily overweight.

Ultra light caravans – chassis

Before designing and building himself, Glenn approached many caravan builders. All claimed it could not be done. ‘Aluminium tends to break mate’. Indeed it does. But, as Glenn points out, steel used incorrectly may also break. He suggests anyone truly believing aluminium used correctly breaks to ‘bear in mind that Boeing 787s are hardly based on rolled steel joists’.

glenn Portch main chassis web

Partially completed main chassis – the triangulated design is clearly seen. Pic: Glenn Portch

Some trailers have alloy chassis – but of ‘C’ section, or I beams 6-10 mm thick. Their resultant weight and poor torsional rigidity, however, defeats the point of using it. But it’s good promotionally.

Glenn 2014 (7) diagonal bracing

This end view of a partly-completed ultra light caravans chassis shows triangular bracing. Pic: Glenn Portch.

Glenn Portch’s concept employs ultra light three-dimensional trellis-like chassis of light box section aluminium. A composite material floor, and a similar (frameless) body bonds to that chassis. This allows slight flexing to cope with road irregularity stresses. His ultra light caravans are thus similar to aircraft and ultra-yacht design. It enables his aim, of about 200 kg/metre for fully equipped units, to be achieved.

Ultra light caravans – strength

For any doubting the strength and durability of this ultra light caravans approach, consider this. The first (of eight) Glenn built has already exceeded 300,000 km. That’s hugely more than the average caravan’s 13,000 or so km a year.

Ultra light caravans – interiors

Glenn’s overall ultra light monocoque concept handles forces via the external skin. Internal fittings too structurally brace. Floor, shower and divisional walls, are all MonoPan. This is an ultra-strong fibre-reinforced thermoplastic skin bonded to a similar core. The outer skins provide structural strength and resist impact. An ultra-light core separates the skins, enabling major resistance to bending.

The cabinetry’s cube-lock square aluminium extrusion is held together by plastic corner locks. These are riveted and glued to the main structure. This, working in unison with the monocoque shell, further adds strength. Glenn makes the drawers of 1.6 mm aluminium. Runners rivet in place within the cube-lock structures.

Bench tops are 30 mm Monopan, laminated, and with Jarrah timber edging. The Monopan is finished inside and out with automotive two-pack paint. ‘It withstands weathering better than bare fibre,’ says Glenn.

Glenn 2015 unit complete small

This is the last and lightest built of Glenn’s builds. It is 9.1 metres – yet can be built at under 2000 kg. Pic: Glenn Portch.

Ultra light caravans – the last and lightest

The last built (in 2015) is 31 ft (9.1 metres). It is far from an average fifth wheeler (that typically has a 100 litre plastic water tank and cassette toilet).

This one is sumptuously fitted out. It has 380 amp hour battery capacity, plus 450 watts of solar. The 1500 watt Trace inverter has an inbuilt 75 amp charger. There is a 219 litre compressor fridge, 400 litres of freshwater, 300 litres of grey water, plus 220 litre black water tanks.

Without its AL-KO suspension the chassis weighs a mere 200 kg!  Had a traditional 19 mm plywood floor been used, that alone adds some 200 kg. Yet has zero structural strength. It also necessitate a heavier chassis, wheels, tyres and brakes to carry it. All add yet more pointless weight.

Glenn bathroom basic web

The completed unit originally weighed under 2000 kg! The buyer, however, sought heavy additions, including dining, vanity and bedside tables of solid Jarrah. Also sought was a full-size double domestic sink and 6 kg capacity washing machine. Plus a china toilet and macerator. There is also a hospital-grade vinyl floor. It weighs as much as the 30 mm Monopan it covers!). Required too was a slide-out BBQ, beneath a 5.4 metre awning.

Glenn 2014 (5) gas bottles web

Gas bottles are set within the chassis rails. Pic: Glenn Portch.

Despite all this, the unladen unit still weighs only 2260 kg. Its permitted on-road weight, however, is 3800 kg. This leaves an extraordinary 1.54 tonne for water and personal effects!

 Ultra light caravans -proving them possible

Glenn was constantly asked to build ultra light caravans for general sale. His main aim, however, was to show (and prove) what he felt possible. He did not do this for profit, but intellectual interest. Developing and proving the concept took over 20 years. That he has now done. He considered consulting if any manufacturer was interested. But, as of early 2017, none appear to be.

Now, by and large Glenn enjoys using his own. At the time of originally publishing, he was enjoying the Australian winter up in the tableland outside Cairns.

I thank Glenn Portch for so generously sharing his knowledge. This article has already inspired self-builders.

Meanwhile, local caravan makers may need to start thinking hard about light caravans. The era of heavy tow vehicles is passing.

Ultra light caravans – further information

For further information on fifth wheelers see Also The topic is covered also in the Caravan & Motorhome Book. My other books are: the Camper Trailer Book, Caravan & Motorhome Electrics, Solar That Really Works (for RVs) and Solar Success (for homes and properties). For author information click on Bio.