Years ago my hubby built me a box out of 1/2" plywood. The dimensions were 4' long by 30" wide by 30" high. The lid had a 6" lip all the way around which raised the overall height of the box. Two 1x4 boards forming a V were set in to run the length and would hold a western saddle with room to spare. Cleats ran around the inside of the box and held a tool tray. By putting the cleats all the way around I could slide it along rather than set it down outside the box. The lid had room for saddle pads or blankets held in with webbing. There was room beneath the saddle for all kinds of stuff. Stout handles were installed on the outside made of 1x4's which ran the length on the outside, better for balance and easier on the hands as the hand parts were rounded a bit and sanded smooth. A rod was installed on the bottom at one end as an axle and two lawn mower wheels were installed. Ah yes, almost forgot. A stout hasp about 8" long was installed. It took two men to lift the box into the back of a pickup so not an easy item to steal. It was painted bright red, easy to see.