The trailerable houseboat with slide-outs is made with a German composite material called Monopan ™ and with a clever system that uses an air compressor to slide out the pontoons and boxes. A friend of mine builds 5th wheelers with slide-outs and we adapted that design for our proto-type.
Our design was slightly more complex as we planned to bring the whole pontoon out with the box but the principle stayed the same. So all of the building materials had to be light weight and resistant to salt water. The only material used are plastics and alloy and very little stainless steel. No timber, no fibreglass, nothing that will rot in either sun or water.
We have learnt a few things by building the first one and would perhaps go a little smaller next time but size is always a compromise when it comes to comfort in your layout. This model is 8.40 m or 27 feet long and features a separate toilet and shower cubicle, 2 click-clack couch beds, full kitchen, solar power, 360 amp hour house batteries, large fridge/freezer, large pull out pantry, 450 l of fresh water, 150 of grey water storage, 60 litres of fuel tank, and a 60HP Honda 4 stroke engine. The pontoons and centre hull are made of 3 mm high tensile Aluminium by a local boat builder Mark Tirrell from Noosa Marine Repairs. The slides can also be pushed out on the trailer and the boat used as a caravan.