Best base for a custom hoverbike?

Posted in Custom Workstation

I'd really rather not spend tons of money hunting down 3 different bikes to spend hours dremeling on (despite that if I had the money and time, I would). But I feel with the way I work on my customs, that it'd be easier if I could just build it all and do it all from a blank slate more or less.

I'm looking to make these:


All 3 bikes will have different things about them, but that's not what I'm worried about at the moment. I just want bases to work off of. That was really the best picture I have offhand of them, but essentially the front is a smaller sphere shape, while the back is a bigger sphere shape with four huge tailpipes sticking out in a square sort of formation (one on the upper right, upper left, lower right, lower left sections of the back).

The only thing that really comes to mind would be styrofoam, but would that be the best choice? I do a lot of sculpting when it comes to my customs anyway, so I'm not too worried about that, I just don't know if there'd be something better than using styrofoam. And does anybody have any recommendations on where I could find a lot of styrofoam? I know Hobby Lobby sells some, but I don't know if it'd be big enough, as they have to be in scale with 8 inch figures.

Thank you very much!