coat them in some Coppertone, SPF 30 at least.....
that was a joke (i have to be more careful and make sure people get that i was joking). i don't really see it as being too much of a problem as snakes don't have skin like humans, there scales are made to protect them from all sorts of things including the sun's rays. i would worry more about yourself sitting out there for too long with your snakes.