Good deal, I hope! One bit of advice: Get someone qualified to check out the hubs and bearings and make sure everything there is properly greased and adjusted and good-to-go. If it has new tires, there's no telling how many miles it has on it. Bearings and maintenance are cheap compared to a breakdown. Make sure the tires are trailer-rated.
Hose it down and check for any little leaks in the seams or door gaskets.
Don't forget ball lock, hitch lock, door locks, etc. It's a rough world out there.
EDIT: Is this the TKO Graphix?
http://www.tkographix.com/