Not all adhesives need super strong clamping to adhere properly. If you choose one that doesn't need a lot of force, particularly one that's fairly fast setting, your clamping arrangements get a lot simpler--potentially just having a few friends help hold it for a few minutes or rigging up some weights or something.
I've heard of using spray foam to adhere the luan (or whatever) to the styrofoam insulation, assuming that's the core material. Relatively low expansion ("window and door") foam would probably work best. That has the advantage of having very good gap filling properties. I've used thickened epoxy for this sort of repair with seeming decent success; construction adhesive (if compatible with foam boards--some may not be) would also be a reasonable choice, though harder to spread evenly. For the Filon to luan bond, contact cement might work acceptably and requires only a good rolling to get a strong bond.
If you have a front window on the cabover, you could perhaps remove it and use clamps that go through the window hole.
