A lot depends on how you plan to use your 5th. Rolling down the highway in and out of RV parks, flat driveway at home you can get away with minimal 5-6". If you plan to get off grid a bit on bumpy roads and/or if you have a steep driveway or place you park you need more clearance. I have 7.5" and it's barely enough for my driveway (slopes down from the street). A slider hitch can sometimes help on changed in grade. The underside of my 5th comes close to the back corners of my pickup bed when backing in beside my house but when I slide it back it clears much more easily.