Find a place that services golf carts. They will give you the worn tires and rims for free. Since you don't need or want the tread(extra weight) these work great. I used to use a PVC drain fitting that I could bolt to the rims and was greased to slide on a aluminum pipe. You can make cradles but turning the boat over and using the hull for a mold. But trax will always work better and ater I had used a set of homemade for a couple of years I just broke down a bought a good set. They lasted 14 years( money well spent). Check craigs list and some of the sites and you might be able to pick up a set cheaper.