96...
Does your gen batty have an on/off switch?
If so - you might consider replacing it w/ a off-1-2-all switch. and doing the same cross connection you mentioned. I have a similar situation and have the new switch to be installed this spring (same mtg /bolt holes and needs one jumper to be added. This will allow a great deal of manually selected flexibility - charge gen batty from alt while running, from batty charger, also allows using start / house batty to start gen or gen batty to start main engine.
David's suggestion above will do the charging automatically.
FYI - if you choose to go the combiner route...
There is a
Reference Mat'l thread in this sub-forum
Article: Battery Isolators & Combiners that includes a
Link To The Sailing Today Article This outlines the many different options for combiners along w/ some +/-.