We do "modified" navy showers. Quick rinse, shut off shower, soap up, then take our time rinsing off. As others have mentioned, hot water heater, even though only 6 gallons, lasts a surprisingly long time and is quick to reheat.
Our TT's shower stall is quite small, so not too comfortable for long showers... and for better or worse, absolutely no room for two people...
Grey water valve we leave open when hooked to sewer. Close it the day before leaving to fill the tank a bit so I can rinse the stinky slinky when dumping the black tank the next day.