I agree. Add something like a rockpile at one end, not enough for them to get all the way out but enough so he can lay on the rocks mostly submerged but still be able to breathe (without swimming/stretching).
I guess there are a couple factors. We built a new house and moved three years ago, I had a lot more up and running before that. The second reason was that I started getting really into my reef tank, so I kind of phased out a lot of other setups.
I built a barn (24' x 36') last summer and am going to pour a floor this summer, hopefully I will have my fish room going within a year. After that... Goodbye empty tanks!
Snappers do get quite large...the largest I've trapped here in NY (for a field study) is 32 lbs. with a SCL of 20.5 inches. If you are serious about keeping one check out these two links: Chelydra.org - site specificly relating to keeping snapping turtles
Turtletimes.com - Snapping turtle 400 gallon tank topic