If you dont mind me asking....how much was your hot water system all fitted?......its something id definitely be interested in as we will quite often be off grid and I do like the idea of having hot water and the ability to have a quick shower.
On price of water heater, I can't give you a precise figure. However, the complete conversion from new LWB 150 T6 DSG Highline to our specification was close to £55k. So this included hot water (including temperature variable shower), underslung LPG -15 litres, flushing toilet, LPG heating, upgraded media to include campervan sat nav, led daylight driving lights, leisure battery, led internal lights, wind out awning, high top, fridge, hob, oven, solar, VW towbar, more storage than we know what to do with, swivel captain seats, crash tested bed (2 singles that fold down to give a full width double), extra sound proofing and insulation - you get the idea. Conversion by an approved VW converter, full VW warranty on vehicle and 3 year on the conversion. I suspect that a fully installed hot water system like ours would be in the range £1500 to £2000 - not cheap as I said. While ours is not a Cali, a Cali does not work for us, we like it better than all the Calis we have tried. Ours will not suit everyone by a long way.
Pictures;
Can see the LPG tank behind the spare wheel (this won't work on a 4 motion), and the water heater is under the the rear nearside passenger seat. Not sure one could put the heater underneath the van as it is likely to freeze in the winter - we go out a lot in the winter.
For the controls, on left is water level, middle gas level and on the right the water control, 2 heat levels on 240v, LPG and a frost stat. Underneath is the shower connection.
If close to Gloucestershire you are welcome to have a look post lockdown.