I'm guessing its made of 1x2s, 2x4s and 4x4s, if im wrong or if theres a certain type of wood to use than please tell me.
You guessed right
This stand was also designed to suit a 50gallon.
put a layer of mdf over the top of the stand underneath the foam just to help smooth out any discrepencies in the woodworking (Not that i'm suggesting there will be) and counter sink screw it in.
How much weight is in the snake tank, you could get away with something like 1x2 or 1x3(if it's available?)for the shelf if theres not much weight in it. otherwise I would go 2x4 for the whole lot.
and how wide is the 30g? You probably won't need the horizontal braces running the length of the stand in the centre, just use the one in the centre running front to back. might save a couple bucks.
hey if you can find something slightly smaller then 2x4, like 2 x 3 use that instead. It will hold.