Avoid mdf like the plague. It's too heavy, its brittle, its a pig to work (compared to ply), and wet for any length of time it turns to mush.
Best using 1/4 and 3/8 inch ply. You can make some real weight savings by being careful with material thickness and using clever ways of adding strength.
I based my 110 load carrying around green plastic boxes from Viking Direct, placed on a sheet of 1/4 inch ply with foam sheet under it for insulation and noise deadening. Something like these. but not exactly the same - cant see them on Viking's site but they might still be there.
Basically I made a configuration of the boxes using different sized ones to fill the available space, then built the wooden platform above out of 3/8 ply for sleeping on, to those dimensions. By adding a few softwood ribs under the sleeping platform I was able to strenghen it, but it relies on the plastic boxes for its real strength - sufficient for three adults to sleep on without bother.
By careful design I was able to use the boxes when taken out of the back as seat bases with thermarest chairs on, and also using one of the pieces that span the back as part of the sleeping platform, sat on two of the smaller boxes and made into a table.
The advantages of plastic boxes are - they're cheap, they're waterproof so if something bursts or spills it wont soak the whole interior (you dont want to soak your interior with milk - in the tropics thats awful), or oil or brake fluid or whatever else.
Careful use of tie-downs and metal angles bolted on each side under which the sleeping platform ply can be slipped will ensure that when you bounce it wont all go airborne.
Best using 1/4 and 3/8 inch ply. You can make some real weight savings by being careful with material thickness and using clever ways of adding strength.
I based my 110 load carrying around green plastic boxes from Viking Direct, placed on a sheet of 1/4 inch ply with foam sheet under it for insulation and noise deadening. Something like these. but not exactly the same - cant see them on Viking's site but they might still be there.
Basically I made a configuration of the boxes using different sized ones to fill the available space, then built the wooden platform above out of 3/8 ply for sleeping on, to those dimensions. By adding a few softwood ribs under the sleeping platform I was able to strenghen it, but it relies on the plastic boxes for its real strength - sufficient for three adults to sleep on without bother.
By careful design I was able to use the boxes when taken out of the back as seat bases with thermarest chairs on, and also using one of the pieces that span the back as part of the sleeping platform, sat on two of the smaller boxes and made into a table.
The advantages of plastic boxes are - they're cheap, they're waterproof so if something bursts or spills it wont soak the whole interior (you dont want to soak your interior with milk - in the tropics thats awful), or oil or brake fluid or whatever else.
Careful use of tie-downs and metal angles bolted on each side under which the sleeping platform ply can be slipped will ensure that when you bounce it wont all go airborne.
