Here is what I did for my Frandee. I have a 16 ft car hauler trailer with 3500 lb axles and side rails that are just over the wheel fenders. I built two boxes out of 2 x 12s and 3/4 plywood, they are each 2 ft wide with the back end ramped down. I added cleats to the up ramps to allow the tracks to grab. I was worried that the plywood top would get slick so I went to our local farm supply store and bought 3/4 inch thick rubber that they use for animal stalls. I attached the rubber with short grabber screws (the heavy outdoor type) and stainless washers to spread the load out. I did not screw the boxes to the deck, but instead used two spacers, one front, and one rear, that wedge the boxes into the side rails. I also have the ski mounted between the boxes so there are additional supports I did screw to the trailer deck, but you probably do not need that. One thing that is bad about the Frandee is that the undercarriage collects a lot of snow and once on the trailer it falls off and builds up after a while. One nice thing about my low deck and the ramps on the ends of the boxes is that I do not need to use the ramps to load or off load. To off load I can just back off the trailer, to load I put a short 6 x 6 in front of each track about 2 ft behind the trailer, the cat climbs up those blocks and bites into the trailer. I added stop blocks so I alway load to the correct front-back location. With this set up I can off load and load in 5 minutes, including tieing it down. Works well for me. Oh, one other thing, with the cat up high like this, I have had somewhat slick rubber surfaces, you must be very careful when loading so you don't slide off the deck, that would be a bad day for both you and the cat. I always make sure my deck is cleaned of extra snow and I try to keep it level (side to side) so I don't slide off. Oh ya, one other thing, the cat sits very high up, I think mine is at 10-1/2 ft, well above the truck, I worry about taking a rock in the cat windshield when driving down the highway, so I am going to make a plexiglass protective cover to go in front of the windshield when I am traveling.
