I just searched out this thread because I moved my camper to a new truck and it squeaks terribly. So I'll try the 2x4 thing. But on the tie-downs, do I even need spring loaded tie-downs? Why not simple turnbuckles and use good judgement to not overtighten them? Convenience isn't a factor -- I don't remove the camper.
You'd be better off starting your own thread instead of dredging up one that's been dead for 3 months.
There is some flex in your truck and the spring-loaded tiedowns give a little.
Simple turnbuckles will transfer the forces to the next point of "give" which is the camper frame. That could cause problems IMHO.