In fact, lets take it one step further. What about a portable hot tub on that next deployment? Sure, it's not within regulations, but it wouldn't be the most ridiculous thing I have seen at a deployed location.
The Nomad Collapsible Hot Tub comes with a 60-inch diameter, 225-gallon vinyl tub and appears to comfortably fit four adults. The tub and frame fit into a 16x16 inch dry bag.
It won't come cheap but it is a portable hot tub. The tub and frame will set you back $550. The water heater coil costs $625. The buy them both, it will cost $999.
About that coil. The stainless steel coil can heat 100 gallons of 50 degree water up to 100 degrees in roughly an hour.