I would be amazed if a handheld GPS required 12W of power - that's as much as the whole empeg uses.

Anyway, the RA line has an auto-reset fuse on it, so you shouldn't cause yourself any hassles if it did. Just remove the GPS and the fuse would reset. So you should be able to test the theory. I'd still check the specs / do the calculation, but that's just because of who I am...