Need info on what to do with possible gravid female king/corn hybrid...

my king/milk hybrids mated several times in early march(about a week before to a week after 3/6/11). if she is gravid, should i be able to tell yet? I know i need to give her a separate area in the tank with some soft/moist substrate so she can burrow and lay eggs, but what should the substrate be? sand, vermiculite, topsoil??? Please help! I love these snakes and am really anxious to see what their babies will look like. I have a solid understanding of how to incubate the eggs once they are laid, and how to care for hatchling snakes, too. i just don't know anything from when they've made whoopee to when the eggs are laid! Thanks so much for any and all responses.

Thiese are pics of the snakes in question. I got her(and her cagemate) from a carnie...long story...had them about 8 mos. They've been great snakes, mostly calm. male is a little more jittery than the female. I was told that the female is a milksnake/kingsnake hybrid and that the male is king/corn/milk. I don't know if that's actually possible, but either way, i like the snakes! first pic is female(Apple), second male(Patches).