Old Boater

B&Q are selling their own brand of plastic fittings guaranteed to -20C. I know you'd still have to drain the pump etc but would make draining down pipework a bit pointless!

I have a Dickinson cookstove on my boat, which is similar I imagine. It was a lengthy job to both fit a small diesel pump to feed the stove and the waterworks (and circulatory pump) to feed a rad. I have a fuel tank for this right up in the pointed bit of the bow, which turned out to have a huge capacity. It works well apart from being impossible to dip, so, with hind sight, I would fit some sort of gauge. The stove is heavy (although not as heavy as yours, I'd guess) but is balasted OK. Kuranda Marine have all the bits - pumps, chimney etc - and were very helpful with advice, so I'd try them. Dickinson have a web site with downloadable manuals which may also help.