[Stripit]

You don't say where you are but I would find a fabricator either on Craig's List of possibly a custom car re-builder and sketch a drawing of what it is you want. Have length, width and height measured out and they will be able to give you some figures of cost and time to build and maybe even tweak your design to better suit your needs. Even a welder shop can do this type of fabrication. I would have it built with the trailer in their possession so it will fit correctly and be able to be removed as you need. It will cost more than any already made flimsy Chinese unit, but you will have something that will work and last without breaking apart on the first trip.