Boat trailer mods

I just purchased an older bass boat (89 champion) and the trailer is one of those that sit really low. When hooked to my truck I am dragging the back bumper real bad. So I am in the process of changing the how the axles sit on the leaf springs and getting it up off the ground a little bit. My question is how much ground clearance is enough? Or how much is too much?
I have a Dodge 2500 with a 6" drop hitch and where it sits right now, the trailer has 5" of clearance, so I’guessing I need about 8-10" of clearance.
Sound about right?