I'll second the hardboard recommendation for a project like this, or for extra lightness go with corrugated plastic board (sold in 48x96 as well).
I get the wanting to make it out of easily transported and smaller pieces, but I think you're going to run into creasing and unwanted folding if you go that route. A rental truck isn't ideal, sure, but nobody in your circle has a pick-up that you can buy him/her lunch for the trouble? The corrugated plastic and (to a lesser extent) hardboard have some flex… maybe you could even fit either of those into a larger Jeep-style vehicle.
That said, if you go with the corrugated plastic you could have them cut 1 sheet into 2 (2x6) and 1 into 3 (2x4) pieces and glue them together (opposed) for extra sturdiness. If cut with a razor knife they have very little fraying (if at all). It'd still be worlds lighter than plywood and not have any creasing. You could probably fit those in your car. They're cheap too. ~10 bucks a 4'x8' sheet.
So it goes.
Last edited by 709 : 2014-03-03 at 16:59.