I built a 5 x 10' lat year with a 5000# capacity. I bought the plans on the internet for it. The plans called out for 1 4" cylinder to dump it. I modified the plan to use 2 - 2 1/2" cylinders. I wanted 2 cylinders to KEEP it from twisting. The hinge is approx 18 inches from the rear of the trailer.
The trailer works great, but I would change several things,
1. I would use a sissor lift
2. I would make it as wide as possible (I load my
BX22 on it, but I have to remove the mmm every time i load it)
3. I would make it power down, I have a flow control on it to regulate the speed when it is lowered with a load, but when it is cold out (Michigan weather) it lowers toooo slow.
Ok, sissor lift vs cylinder: In my humble opinion, the sissor lit would give you more dumping capacity, plus incresed dump angle (45 deg vs 50+ deg) becuase with the cylinder type the cylinder is laying almost flat, with a HEAVY load, the dump box does not want to start dumping (it is pushing almost strait against itself). The intial "breakover" is incredible.There have been times when I have had to help the box up for the first few inches.
The sissor lifts ae designed to accomadate this, thats why they are on dump trucks.
Sorry for the long post.
Hope that helps