Hitch Weights (w/LP & w/o options, water & cargo) (lbs.) is 350lbs
Unit Base Weight (w/LP & w/o options, water & cargo) (lbs.) is 2860lbs
Gross Vehicle Weight Rating (lbs.) is 3500lbs
FJ shouldn't have any problem towing. Have considered the next up size like you, for the separate shower and holding tanks, but I think it would be too close to limits, which is okay for a while I suppose, but we don't have plans on swapping out the FJ anytime soon. We do like to offroad some, so I may eliminate the airbags from consideration and just focus on the springs.
All I need now is a hefty deposit to the toy fund for more mods!