I have a kayak rack from RVkayak Rack.com that I use on my 24foot motorhome. I haul two 12 foot kayaks and two bikes. The rack is designed so the top is 13 feet high which is within the federal limit of 13'6". I have no problems with any highways. I am careful on back streets with limbs, but that is very rare. There is some bounce on rougher roads but after 3000 miles no problem. I looked into many different alternatives including a custom rack but the way this company makes the rack to your measurements, it is essentially custom made. I have been very satisfied with the rack which is of excellent quality. Talk with them and see what they can do for you.