So I got to try the the new casters on Saturday and they worked excellent on the road.
The only flaw I experienced with this design was when I had to get onto the uneven soft shoulder because of traffic my ski and tub portion of the sled wanted to lift up off the 2x4 cross members. This was most likely caused because I was still pulling the rope from the ski tips causing some lift and the extra drag from the softer surface. I did not have the sled strapped in anyway to the 2x4’s (just had the weight of gear on them) . The casters still worked surprisingly well on the soft gravel shoulder .
I had to stop a couple of times to push the ski/tub portion back down flush onto the lag bolts through the 2x4’s.
Just though I would share so anyone one looking to add casters to thier sled the same way can lick the problem before heading out. I’m sure a couple straps in the right place will solve the issue.