moving up to a bigger tank

so im planning on get a leopard gecko, i have my bp in a 20 long, i have a spare 20L and have a 30 for my bp when he is full grown. so my question is on trying to save money, since im gonna have to buy a UTh for my leos, and eventually the 30 gallon, can i move my bp up to the 30 gallon, so i can spare buying 2 UTH, one for my other 20 long and one eventually for my 30. yea thats a mouth full but wanted to explain/ my bp is probelly about 16 inches now. i have 3 hides for him in the 20, and i just spent 25 bucks at wall-mart on fake plants leave and vines. would it stress him out, or would all the cover help him like it.

He is way too small for a 30 gallon! You try dividing the tank in half with cardboard or something. A 20 gallon is even a little big. Why not put your geckos in the 30 gallon until your ball python is big enough.

hey i didn't think of the dividing part