Hi,
Thanks for the advice, Hiace4wd. I'm keen to stick with a solid state unit, though, rather than introduce something electromechanical. Would be nice to improve on the old diode-pack, though.
While researching, and trying to find a price for a solid state split charge relay, I came across a FET based charge splitter on eBay for sensible money. It's one of these:
https://www.victronenergy.com/battery-isolators-and-combiners/argo-fet-battery-isolators
...and looks like it should do what I want.
Will feed back in a while, once it's in and working.
Cheers,
W.