The Gumstix is extremely compact, so fitting it inside the wing should not be a problem. Extra insulation will probably be needed, and we will have to work out how thick it should be and what materials are best. Batteries will be as far forward and as low as possible so they will not crush anything on a bumpy landing.
I may modify the servo mountings so the top of the servos can be insulated.
The parachute and balloon can be attached from the rear with the load spread out over the main spar. The parachute can be stored in the cutout for the prop at the rear.