I’ve hauled a Carver Cascade 2 water heater out from our donor caravan for our campervan build. These combination gas/mains water heaters have been common place in caravans for years and little has changed. Parts are pretty easy to obtain and the unit can be services and maintain. There’s a handy service guide for them on Practical Caravan.
Ours is in pretty good nick having examined it today; that said it will need to be test run on the bench outside first, then cleaned up before install. I see no sense in cutting a square out of the side of the van only to find I need to rework the install!
I found a handy resource for anyone looking to use a Carver Cascade heater online at Arc Systems. I’ve replicated the documents on the resource pages for anyone else that wants them and will add anything else that I find that’s relevant.