Dave Plowman (News) wrote:

I was considering fitting one permanently to the old Rover,

Why? It's an (slightly) old Rover, but it's a modern battery. Should be
no more susceptible to cold-start problems than anything new, assuming
it's in reasonable condition and you have an ignition system with some
sort of inverter that's less susceptible to battery voltage than plain
coil+points. The Rover V8 is also a pretty easy engine for
cold-starting, so long as the fuel lift pump isn't the original SU
(IMHE experience on 4x4s).

The question is what would be a suitable weatherproof connector
for this as the car lives outside?

Bog standard big round blue one, otherwise it's weird and thus a bad
thing. Given the choice between finding somewhere to stash a big one
and using a little one of dubious reliability in bad weather, then I'd
choose the standard.

There's probably some variant of an XLR that you can use, for
sufficient money.