Squat don’t mean squat
when it comes to bed rail clearance. The trailer and the truck bed are going maintain the same clearance wether you have 5 lbs on the pin or 5000lbs. If anything the tailgate top to camper bottom might increase minutely. I agree you need at least 6”. I have around 7 and there is one place we have been to twice that has a very tight hairpin turn in the campground that I have to drop my trailer wheels completely off the road on a fairly steep slope and I probably get within an half inch of hitting the bed rail. After the last time I decided that if we go there again I will back down the one way road instead of attempting that turn. It would be less stressful!