That sounds feasible -- but expensive. I would check for the availability
of a feed lug kit first, or move the dryer circuit to the new subpanel to
free up 2 slots in the main panel.

If the main panel is surface mounted, you can attach the subpanel to its
(hopefully) side knockouts with a 2" rigid conduit nipple and a few lock
nuts; it makes a neat installation.

Bob

Unfortunately the panel is recessed into drywall but fortunately, I'll be
putting
the subpanel right next to it (with a stud in between) so it shouldn't be
too difficult.

As far as I can tell, the only added expense I would have for what I had in
mind
vs. the feed lug approach would be the quad breaker ($25 or so online).
I'd still have to purchase the
sub-panel and breakers for it anyway. With your solution I'd have to get
the feed
lug kit but not sure what they cost. Am I missing something here?

Thanks for the help Bob!
cc