I would not be so quick to step away from the good ol'
relay (or starter contactor, if you need big current and
not continuous duty). Isolation is a freebie, replacement
is easy, thermal concerns are about nil and so on. You
can probably find a lot of info in this vein on RV sites as
these tend to have multiple batteries to manage.
Sure, you -could- do it solid-state. Maybe even at par
on cost. But what, besides a little coil current, would you
hope to gain?