My two pesos:

I have been using an Interstate standard full-sized (group 41) battery for
four years, count 'em, as my auxiliary battery. This battery is dedicated to
my Propex furnace, which runs sometimes in the winter all night long,
practically draining the battery when I've been stationary for more than one
day. The battery charges up just fine, and has gone through many, many deep
discharge cycles. My view, therefore, is that a standard battery is just
fine. Oh, and last winter Olympics, I watched TV for hours each evening,
while the furnace kept me toasty warm. Optima Schmoptima. Mine works just
fine, if it fails I'll buy another and still have less than the cost of one
Optima. OMO, YMMV.

Karl Mullendore
Westy Ventures
1987 Westfalia Syncro 1.9TD