I have a solution
Well, after nearly a month of research, I have a solution on the way. I have always been concerned with touching the vehicles coolant system, and more concerningly running coolant lines all the way back to the bed. I also did not want to run the engine because the tent is just above the exhaust. This cool little water heater is electric and will run off of my inverter. While driving, the inverter will power the heater and bring the water temp to 170 degrees. One gallon of 170 degree water will provide enough water for at least two (longer) showers as the shower has cold and hot inlets.
Hot water heater: Hubbell CE-110 450
1 Jacket Blue-Green Enamel
2 Heating Element 450 Watts, 120V
3 Thermostat 110-170oF
4 Stainless Steel Tank - 1 Gallon
5 Hi Limit Manual Reset - 190oF
6 Access Plate To Hi-Limit
7 Cold Water Inlet - 1/4" Male NPT
8 Hot Water Inlet - 1/4" Male NPT
9 Front Cover
10 Electrical Service Entrance
11 Insulation Fiberglass 1" Thick
12 T&P Relief Valve Opening
Optional Equipment:
Tempering valve to increase the supply of hot water to 11.5 GPH 45-110oF
450 watt model, please specify model CE110-450 W rated 4 amp at 120 V
Notes:
Unit rated for 150 psi WP
Recovery rated 6.3 GPH 45-110oF and will draw 8.3 amps at 120 V, 1 PH
Unit supplied with two (2) wall mounting brackets
Unit supplied with T&P relief valve set at 150 psi and 210oF
Enclosure: TePee