Chris,
Totally agree on the Bid/Bin thing, there is a lot a general dissatisfaction with ebay at the moment... I think it may have had it's era. The prices of these thing are a bit less than last year, but not for much longer, I suspect.
I was asking the other way around about the engine, i.e. can you run it with the engine?... I've since found a couple of references that say you can, apparently modern diesels run so thermally efficient that they need these things to heat the heater in general use.
Justin,
A lot of boats use these in the manner you suggest and as part of their central heating, but you may have to wait a while or have a small capacity tank, I'd think.