This is my hot shower setup since 10 years, by using a heat exchanger to get hot water when the engine is running.
Here I did start to collect solutions and components for a hot shower by gas, diesel, 12v, 110v/220v and solar at this link:
Hot water and shower solutions for vanlife, overlanding and outdoor. - [Leaving Land Cruiser Club]
European Market (german):
Heisse Aussendusche - Lösungsansätze für Vanlife und Overlanding - [Leaving Land Cruiser Club]
For portable shower solutions the us market delivers more stuff, for components for DIY Shower Projects, Water Boilers (geyser) - the european market delivers more, therefore both are listened.
Funny to try too get an overview over the international market. Like at example the Ironman 4×4 Eco Pressure Shower from south africa is sold a DrPrepare at the US market.