I'm planning to install an auxiliary battery, though maybe not under the
driver's seat since I can't find a deep-discharge battery that will fit.
(I'm still looking.) Is there a need for venting to the outside if I
install it, say, under the rear bench seat?

Also, I'd like to know the size wire I should use to connect the auxiliary
battery positive to the starter battery battery. (I believe the wire from
the auxiliary battery goes into the relay under the driver's seat and then
from the relay to the starter battery.) Thanks. -- John