Re: Using trailer for shore docking
I don't see a problem with using a trailer frame for a "shore dock" as you describe (not something we'd do around here, with tides and salt water!) and you could even drag the boat up the hill with your car. One advantage is you get to use rollers, which is better than bunks. Problem is, if the water level changes, one way or the other, you are out of business. Thus a long set of skids (bunks) would be better if water changes.
But i do not like the idea of trying to put the dock trailer frame onto another trailer frame to go down the road. There is a long list of problems with that, involving all the professions: engineering, law, medical, mechanical, physics and probably even clergy. Maybe OK to drag the whole rig up the bank for the off season, but then I'd use log rollers.
Once you set this up, consider that trailer gone. So I'd do it with a sacrificial trailer, not a good one.
If you have changing water levels, consider whether you'd leave the plug in, and rely on the bilge pump, or pull the plug, and rely on the lake level staying put, as well as your memory to put it back in. I'd do the former in season; you don't pull plugs on a boat on the lift or, obviously, moored/slipped.