I'm building a trailer luggage box from the left over back frame from a boat trailer for my Jeep TJ. I debated about purchasing a HF 48"x40" short trailer frame, but went this route. In review, I'm not done with trailer frame layout and I've already past the HF cost in hub bearings/seals, additional steel, and I still need 2 4.8x12 4-bolt tire/rims. I'll be adding a Sears CargoX rooftop carrier for now as it was cheap enough ($35 on CL). I'll also keep the smaller tires for now till I can get my box built (better weather).
Anyways, another way of gaining clearance for the taller tires is to lower the suspension. Many trailer frames have drop brackets for the spring mounts. The old Jeep M416 trailer has 2" drop brackets. Its frame is also a 'C' channel design like that of the HF. Just something else to pitch into the design.