First: If you plan on using the on-board shower, Oxygenics, They make shower heads.
IF you do not have a shower head with a cut off button or valve (Not all do) Then get a 1/2 inch shower cut off valve at Home Depot, Lowes, Mennards, Your local hardware, wherever, Standard 1/2 inch IPT thread. The valve you want has male and female ends and is a quarter turn (Ball type) valve.
The best way to shower the kids.. Same as it was before you got that rig, Park shower.
Way larger water heater, Way more pressure and volume .
Home is where I park it!