@EzShot I have seen these tanks on boats and I would have loved to install one like this in my VW. My original plan was to install a tankless propane heater but efficient usage of space became a challenge so I decided against the idea in the end.
I looked at SureCal tanks, but at the time of looking they were a little out of my price range…I was also under a little pressure to get something installed so instead I opted for a 5 litre Truma 240V/300watt immersion tank (used from eBay) which can also use hot air from the diesel heater to heat the water inside…I wish I had been more attentive to planning during the build…or in my case as far as the retrofitting of the tank goes, installed a switch on the dash to switch it on and off because as things are I need to stop and switch the heater on about half an hour before I know I need the hot water…but I digress!
I had a browse through the forum and found the following thread which mentions SureCal calorifiers which may be of interest to you.
In a nutshell…I haven’t had personal experience with them in vans, but it is possible!