I've always found mine to be too touchy to be able to easily set it back at the right temperature. A tiny millimeter of turn is the difference between being frozen and scalded.
I installed an ultra-low-flow aerator on the bathroom faucet, so if I have the flow on pretty low I can just flip the diverter. It uses minimal water but lets just enough through to minimize backflow. Not really ideal, but it works.
I've considered the check valve solution as well. I'm pretty sure you'd actually need one on each side and not just on the hot water side. I'm also not sure if you'd end up with basically all the water coming from whichever side has slightly higher pressure because of the valves.
The ideal solution seems to be a mixing valve like in a residential shower where on/off and temperature control are separate movements, but I've never seen an RV with one.