Please excuse the drawing… wasn’t in a position to take the time to do a full, fancy thing 
I used:
1 - 10’ full depth unistrut (this is the top bar the motors are mounted on
4 - 10’ half-depth unistrut for the rest
- one piece cut in half for the two 5’ sections
- two pieces cut at three feet for the bottom, 10" for the upper beam offset and 74" for the front - repeat on each side
- one full length piece across the front
1 - 10’ half-depth - this is what I still want to add at the back between the legs… they try to fold “in” when I’m pulling plywood across (I store spare in the triangle
Here’s some pictures of what I did at the joints…
I have the top bar “offset” to the front to adjust for material thickness… honestly, so far I’ve never changed it, but…
Where the back support attaches to the front leg
Bottom front… I have a 2x4 stuck between the bottom unistrut and the backboard to hold up the workpiece. I’ve got to find a better solution here, as it sticks out way to far and obviously will snag the sled.
The bottom with casters… this is the weakest/most problematical part so far… this pictures is looking down on the bottom front to rear piece. The angle bracket is boleted to a piece of 2x4 with casters lag-bolted to the bottom of the board. It works, but they try to “twist” too much.
I intend to mount another piece of unistrut (or a 2x4) across the back of this piece between the two legs to hold the angles “apart” at the back. I think this might help the twist if I do it right, and will definitely help with the angled legs trying to collapse “in” when I’m shoving wood into the void space.
And the front assembly…
