I really like the lines of the D90 without the tire on the back, so I decided to make my own internal carrier. Right now it fits up to a 33", but when I take it out to paint it, I just trim the foot back and it will support a 35". On the front of the central post is where I mounted the fire extinguisher as well.

I cut 1" wide strips from 1/4" stock and sandwiched the rollbar using grade 8 bolts. The lower mount that rests on the floor is bolted through the floor to 1/4" reinforcement plate.