I installed one of these a while back to replace the dribble shut off https://amzn.to/3UAmdVC
KES Shut Off Valve Brass Shower Head Valve with Handle Lever G1/2 Water Flow Control Valve Regulator



Works pretty well, total shutoff. When I turn it back on, I just put my hand in front of the shower stream for a few seconds, and it equalizes pretty quickly. Some people install a check valve in the plumbing to keep hot and cold from not mixing right and causing the cold stream.
Another way is to have a thermostat showing the water heater temp and shut off the heating at the right temp for a shower, then use the hot faucet. Thar method has the added benefit of saving propane when off the grid. Cheers, Ray

I also put a shut off valve in the shower, but also added this back flow preventer to my hot water line and it help. Here is a video by another RVer installing his and he has a link to purchase one at Amazon. https://youtu.be/T4lge5JLYn0

100 F was always an ideal temp for me, and always used just the hot water as Ray suggested.

The easiest way to avoid the cold water blast is to let the water dribble out as you wash. Most stock RV shower heads that have the shut-off valve built into them let the water trickle out to keep the hot and cold equalized when turned off, avoiding hot or cold blasts.

I have the exact one that Ray pictured from Amazon. With mine, if I turn it all the way off I will get a hot water blast for a second or two when I turn the water back on. If I remember to turn it back on while pointing the shower head anywhere but my face it can feel kinda nice.