sure, i seal the balsa with sanding sealer before i glass. it prevents the moisture from the polycrylic from warping the wood. another area in which the sealer helps is allowing me to fill in the grain in the balsa. after i seal i water down hobbylite balsa filler and paint it on the wood (across the grain) and then sand. you're going to have to sand after you seal anyway, might as well double up. now you have a extra smooth fuse or wing ready for glass.

and as for sealing the wheel wells the paint won't soak in excessively. have fun.