-Find a Burly trailer for hailing kids on Craigslist.
-Take the carrier and tent thingy off so you're left with the frame and wheels.
-Cut a piece of plywood or shelving to fit the deck of the trailer frame (the existing holes can be used to bolt the wood to the frame).
-Build an upright frame (most kayaks are wider than the wheel width on the trailer) with 1" steel pipe that is attached with flanges directly to the wood deck.
-Extend the tongue of the trailer by cutting it in half, drilling holes that will fit locking pins and add an 18" to 24" section of steel pipe (fints inside the aluminum tubing on the frame that was cut)