Big Mc, I bought a real nice 18 foot bass boat trailer on craigs list for 250.00, went to town with my die grinder, cut off the bunks, winch and everything above the wheels, added my own spars, pvc runners for tandem side by side kayaks for my wife and I, and am in the process of adding two tees that are removeable to hold 2 more kayaks above the ones on the trailer. Lots of room for your boxes and it runs on much bigger tires. The tire deal for me was a big one, since we also like to take the kayaks to Galveston 3-4 times per year. Really nice having the option of just backing down the ramp and floating off my kayak which I continue to make heavier and heavier.
Good luck, hope this helps with some ideas
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