I also tow a travel trailer (not a 5th wheel) and I just put the kayaks a little forward on the ladder racks and I have no problem with the yaks getting hit by the trailer or hitting the top of the cab. If you have a 5th wheel, I saw a guy from Canada who had a hitch on the front of his truck and a rack inserted in the hitch and a ladder rack on the front stake hole of the truck bed. He put the yak in the center of the truck so that when the 5th wheel moved, it swung away from the yak. Hope this helps.
Charles Robinson