I know what you mean about gallons - I'm from England and I have no idea of gallons! I have an adult male leachie, he's 15 inches and weighs in at 260 grams! I have him housed in an all glass vivarium with sliding glass fronts. Its 48 inches tall x 30 inches long x 24 inches wide. This seems adequate for him. I also have a 1/2 grown female in a 36 inches high x 24 inches long x 24 inches wide, she is in an all wooden viv. I prefer the all glass because Gandalf likes to hid at the back and you can still view him from the sides. Also the humidity is better in all glass.
Got to warn you though, if you get a leachie don't stress to much about the amount of food they eat. I'm lucky if Gandalf touches his food more than once every 10 - 14 days! He seems ok and has a stable weight so he obviously knows what he likes!
