Many people design and build to do something better and/ or cheaper than before, but few spend 20 years doing so with no financial motive. Long-term CMCA member, Glenn Portch N10690, the subject of this interview, has done just that. In so doing, he has shown just what can be achieved in the fifth wheeler and general RV area. It all started in the 1980s when Glenn sought a pair of up-market loudspeakers – and decided to build his own.

Collyn: There was good product in that era – what caused you to design and build them?

Glenn: I searched the market but most of that available was absurdly priced, black only (or both). I used the best available components within a gloss white enclosure with black granite overlays. I showed them to a friend (who owned a Hi-Fi shop) who asked if I could build more.

Collyn: And you did?

Glenn: Indeed, within a few years my then partner and I were exporting our Audio Definition loudspeakers to nine countries and had 14 local dealers. We set out to build the world’s best, and apparently succeeded. They won many world awards during the 1990s but were not cheap as their sound quality, required components and cabinet finish demanded years of research. There were lower priced units – but the top ones were $35,000 a pair.

Collyn: You then set out to build your own fifth wheeler. I recollect your reason for doing so was similar.

Glenn: I’d spent a lot of time in the USA researching audio and the fifth-wheeler concept over there was rapidly gaining acceptance. I liked the idea of travelling around Australia in my own (their inherently stability appealed to my limited grasp of physics) but what I saw had no appeal.

Collyn: In what way?

Glenn: With a few exceptions most back then had chassis that could have been designed in the early 1900s, and used mainly similar materials. Most were almost absurdly heavy and some still are. A few now use lightweight body construction but still end up overweight. My concept was an ultra-lightweight three-dimensional alloy chassis with a composite material floor, and body bonded to that chassis. My aim was to get down to about 200 kg/metre for a well-appointed unit.

Collyn: Did you approach existing manufacturers?

Glenn: Indeed, but all claimed it could not be done as ‘aluminium tends to break’. Indeed it does, but so does steel if used incorrectly. If anyone truly believes aluminium used correctly still breaks they should advise Boeing accordingly – their 787s are hardly based on rolled steel joists. Some trailers  do have alloy chassis – but of ‘C’ section, or I beams 6-10 mm thick. Corrosion resistance apart, their resultant weight and little torsional rigidity defeats the point of using it.

Collyn: What is your approach?

Glenn: A trellis-rail type chassis fabricated from light section square aluminium, and allowing for slight flexing to dissipate road irregularity stresses. It’s closer to aircraft and ultra-yacht design and it works. The first [one] I built has now exceeded 300,000 km.

Collyn: How much weight is saved?

Glenn: My latest (and probably last) is 31 ft (9.1 metres).  Without its AL-KO suspension it weighs 200 kg: complete with the body it weighs 650 kg. Using a traditional 19 mm plywood floor instead of composite, that floor alone would have added about 600 kg – and zero structural strength.

Collyn: You design and built the interior accordingly?

Glenn: Yes, but there’s more to it than that: the overall concept is monocoque. It’s a structural approach enabling forces to be supported via its external skin, but I take this further by using internal fittings as bracing. The floor, shower and divisional walls, are all of a material called MonoPan – it’s an ultra-strong fibre reinforced thermoplastic skin bonded to a thermoplastic core. The outer skins provide structural strength and resistance to impact. The ultra-light core separates the outer skins, enabling major resistance to bending.

The cabinetry uses lengths of cube-lock square aluminium extrusion held together by plastic corner locks riveted and glued to the main structure such that it works in unison with the monocoque shell. Drawers are of 1.6 mm aluminium with runners riveted in place within the cube-lock structures. Bench tops are 30 mm Monopan, laminated, and edged with Jarrah timber. The Monopan is finished inside and out with automotive two-pack paint. It withstands weathering better than bare fibre.

Collyn: What is its final weight?

Glenn: This is not an average fifth wheeler with a 100 litre plastic water tank and cassette toilet, it’s 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 litre freshwater, 300 litre grey water and 220 litre black water tanks.

As I already have my own 11.3 metre unit, I decided to sell this one. The buyer required heavy additions – including dining,  vanity and bedside tables of solid Jarrah, a full-size double domestic sink, a 6 kg capacity front loading washing machine and a china toilet and macerator, plus a hospital-grade 3 mm vinyl floor (weighing as much as the 30 mm Monopan it lays on). There is also a slide-out barbecue beneath an 18 ft (5.4 metre) awning.

It still weighs only 2260 kg. Given LiFePO4 batteries, lighter floor covering and non-solid Jarrah tables, etc. it would be well under 2000 kg. Even as is, its maximum allowed on-road weight is 3800 kg – so there’s over a tonne and a half to spare.

Collyn: How many have you built – and do you plan to make any more?

Glenn: Including my own – that I shall keep – I’ve made eight altogether. I kept a few for a year or two (and then sold them for much what they’d cost to make). I had (and have) no interest in building them for profit. My main interest was in developing and proving the concept over 20 years or so. And that I’ve now done. I’d consider consulting if any manufacturer was interested – but by and large I now just want to enjoy using my own.

Collyn: Glenn Portch – thank you very much for so generously sharing this knowledge. I suspect (and hope) you may have given many a home builder (and RV makers) a lot to think about.

For further information on fifth wheelers (and particularly why they are stable) see http://caravanandmotorhomebooks.com/fifth-wheel-caravans-safer/ and also http://caravanandmotorhomebooks.com.caravan-and-tow-vehicle-dynamics/

Category: Technology
Written: Wed 01 July 2015
Printed: July, 2015
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