John,
Thank you very much,
The leaf springs being rigidly connected - yes that is one of the issues I struggled with in my mind for a long time. As you are so observant to notice, I mounted them rigid. My decision to do it that way reduced the height of the bed by at least 6" and of course allowed me to use the end of the spring for the tilt hinge. But of course the draw back was loosing a lot (most) of the spring action. I have seen quite a few commercial trailers where the springs were rigid mounted, as well as most all Semi Trucks.
Top bracing for the cylinders - good point too. The angle iron that they are attached to at the top is 3-1/2" x 3-1/2" x 3/16" (very stout), plus the floor is bolted to it and the cylinders are close to the edges where the I beams and the diamond plating for the sides are. I figured it would work, and so far so good. As far as bracing for the bottom, the 3" channel does not even budge when the bed is lifted. The bed ID is ~ 50"X100" and the load capacity is around 2500# max. In the video there was about 1500# of wood in it.