HWS

There are now a number of suppliers such as Joolca, Drifta, Kings who sell shower tent bases that allow water recirculation when using these small hot water on demand systems. I haven't used them but much the same as showering in a large container and recirculating.
With very cold water, we have recirculated in a 20L jerry can to get the temperature to an acceptable level.
On another note, our Joolca was used successfully by our son in a Canberra winter when their hot water system died. The system was setup on their deck, connected to the mains and piped into the bath using a potable water hose as the smell and leaching of plasticiser by the hot water from a regular hose was overpowering and likely not good, even if it wasn't being ingested. This worked for the nearly two weeks it took to get a replacement system.

Hi Roslyn.
We have a hybrid camper which I designed and built. We enjoy most of the modern conveniences including pressurised hot water to the kitchen and ensuite. All very nice, however this does place a lot of stress on the water supply.
We only have 130l of tank storage so if top up water is available we can enjoy the privilege. However when supply is short we need to economise as my wife and I can empty that supply amazingly quickly if not economising. We find that a couple litres of warm water in a bucket for a wash will go a long way when water is short. In our case just sit on the toilet seat with the bucket in front on the shower tray and go for it with sponge and soap. I understand your situation is much different but I am making a point here about your husband's concerns around water usage.
We grew up in a bygone era where water was always a premium in our farm houses. Interestingly it was a bit self regulating with the gravity feed from the rain water tanks. When the tanks were full the flow was faster and it was easy to fill a kettle and stand it on the wood stove to heat for a bath. As the tank level dropped the flow reduced and it was usually easier to part fill the kettle rather than wait for it to fill.
Pressurised hot water is fantastic, but you do sort of loose that fifth sense I explained above so you do need to be vigilant around water usage. If you are more than a couple then I would suggest pressurised hot water is a no go for showering and unnecessary for washing up unless a top up hose is readily available.
Enjoy what ever decision you make.
Cheers,
Roy G.

If water temp became a challenge from a low C temp the water can be preheated by recirculating it in a container/ bucket and then shower. Hot water systems in houses usually are 50c or less because of tempering valve so washing up is done below that temp and showers around 40c . I don't see the temp achievable as a problem unless you shower with melted snow.

RMD,

If you have a decent plumber then the tempered water should only be run to the bathrooms.

Cheers Kev