This isn't a mod to the trailer -- but it allows you to pull the trailer and haul your Kayaks all while keeping your bed open for other stuff.
I didn't want to spend the 500 bucks on a Yakima truck bed tower system (or $350 for new towers to go over the cab and I already had the saddles) so I bought a $150 dollar ladder rack.
I welded two pieces of pipe onto the side of each bracket-- and got some "J" bolts. The "J" bolts run through the pipe and down along side the truck's rail-- the J part hooks under the rail and then I crank a bolt down to tighten the brackets down. The bar at the top of the rack puts more pressure against the brackets (horizontally) at the bottom.
They aren't going anywhere and I didn't have drill holes in the truck. To top it off takes me about 5 minutes to remove it!
Then I just installed my old Yakimal Hullyrollers and Mako Kayak saddles via stainless steel hose clamps.
So for a total of about $200 bucks I got a nice solid kayak rack.