Before grouping your two leopard geckos together, make sure that they're not both males. Males should not be housed together, however, you can have several females with one male. They should be similar in size to prevent bullying. For two or three leos, I would suggest a 20 gallon/20 gallon long tank.
If you still wanted to keep them separate, you could always get a bigger tank and just put a separator in the middle.
Put as much substrate so that the geckos can still feel the heat from the
UTH. If you want, you could just stick to one layer of paper towels like we do :P
