You are a tease Mike.

To be brief. Electric only is a far cheaper option than gas/electric combo and one you can do yourself, probably for about £700 now.
I fitted a 10L Propex to my Familia back in 2011. I prefer this to the Truma Therme as it has a larger capacity, variable thermostat and better insulation so water keeps hotter for longer. It is however about 1000w as opposed to 500w, so OK in the Uk but you may need to watch the amperage if abroad.
I fed mine from an onboard tank of about 45L from Catanks. If you are organised and give enough notice then they can chem-weld the in/out/overflow lugs for you at reasonable cost.
I sourced my plastic pipes and fittings from Leisureshopdirect. Use the red and blue pipes and not clear to avoid mould/algea build up.
Clearcut Conversions are good for the switch as they match the existing Eriba electric fittments.
Taps can be expensive. If your van is newish then you may find a Y connector on the pipework just below the tap. If so you are lucky and will not need to replace the taps, saving possibly £100.

Colin