I'm probably going to purchase a bearded dragon next month and I'm currently getting things together for him/her. When I first get it, I plan on using a 20 Gallon long tank. My question is, when it becomes an adult, what would be the best size tank? I can get a 55 gallon tank for 30$, but i was thinking if 12-13 inches wide is to small. I figure it's long enough, but is it wide enough? The measurement would be 48 1/4 x 12 3/4 x 21.