DW and I spent the first year setting shower temp to our preference, mine was 98 and hers 104, plus 120 for washing dishes.
I got in the shower one day and forgot it was set to 120, ouch! So I started mixing cold with hot and it worked perfect, just like at home. So now we leave it at 120 and. mix a bit of cold with hot to get a temp we like.
You do need good water pressure (above 40 psi) and flow from the campground that is consistent. I use 5/8" water hose. It takes several minutes for the water heater to warm up the plastic line to the shower for consistent temperature. Also, don't take a Navy shower, starting and stopping the water heater leads to spurts of cold water, leave it running. Tankless heaters and Navy showers are a good combination.