The only issue I had with my bottom mount was ground clearance. My tt towed fine, but with a bottom mount along with the wd bars, to me ground clearance could be an issue. I have a pretty stout f250 that has a beefy suspension,so the TV was not the issue. I should have measured the clearance but I did not. My unit was born with a top mount coupler, which was defective . The dealer had a local welding/trailer repair facility repair the TT, they installed a bottom mount hitch, the wd hitch had to be adjusted, that was when the ground clearance issue arose. So on their dime they replaced it again with a top mount. Problem solved. The dealer was nothing short of outstanding on this issue. (Dodd RV of Virginia ) I don't see what a few inches could make that much difference but it did.
Chuck " still in Va "
2012 3065w Windjammer
2012 f250 lariat Crew cab power stroke (of course )