How to correct uneven "Bump Clearance" ?

Yeah, I'd just replace the springs with some that are a little heavier. Won't get you any additional weight carrying ability but should raise the trailer frame a little higher over the axles due to less spring compression. You don't want to get too high on the springs though or the trailer will ride like it has no springs.

I recently changed out my 2200 pound springs with 2600 (I think) pound springs and all seems good. Springs are pretty cheap ($100 or so) and easy to swap. I think I got mine at etrailer.com