With RES you should go all out and buy the biggest tub/tank you can get. A 40 gallon wont last you very long and will be a waste of money really. Ultimately you will need at least a 90 gallon - or laarger, so i would just buy something that big to save yourself having to upgrade.

You can buy plastic troughts, large plastic kiddie pools etc for pretty cheap.
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1.1 Bearded Dragons
2.2 Leopard Geckos
1.0 Uromastyx (Mali)
1.1 Corn snakes
0.1 Mexican Black Kingsnake
1.0 Bairds Ratsnake
1.0 Rosy Boa
1.1 Green Anoles
1.1 House Geckos
0.0.2 Flying Geckos
0.0.1 Red Eye Tree Frog