What's the weight of the boat? My 22' only weighs 2300 pounds, and trailers perfectly on a single axle boat trailer rated for 3500#. You may not need a dual axle trailer. Have you looked into borrowing or renting a trailer for the trip? I believe that some marinas/boat dealers will rent trailers.
Here's my Starwind 22 on its single axle trailer, the bunks supports are simple "C" channel bolted to the frame. You could use rectangular tube or C channel to build your own if needed. The second photo shows the bunk supports while I was replacing the rotted bunk boards. It's not very complicated at all. Remember that the bunks don't hold much of the weight of the boat, the majority of the weight rides on the keel support. The bunks typically just provide stability on the trailer.