at work we mold abs plastic sheet over plaster molds and sometimes vacuform over molds.I was thinking with a bit (a lot?) of pre work you could make some reuseable molds to crank out any number of duplicate parts,and if your design was symetrical you would only have to make half the molds since your right rear would be the same as left front,etc..and pieces could be abs glued together.You could even make abs ribs for stifening and attatching interior panels
I work in the theater industry and build lots of cool stuff out of 1/8"ply sometimes bending and laminating plies that are extremely strong and lightweight to carry rapidly offstage during quick set changes. 1/8" ply is usually much higher quality than 1/4" luan and is almost as strong due to that fact
Sorry,just sitting here dreaming of building a mini trailer and thinking with a keyboard in front of me