You wrote:
I have a 95 eurovan and 1st camping trip, using my furnace, by morning, =
the battery was almost completely drained.  Is this normal or should it =
last longer than overnight???  Started the furnace at 10pm and by 3am, =
low battery...

I've replaced my auxiliary battery and it lasts a number of days with normal
use of camper equipment including furnace. The service life of a deep cycle
battery is much less than an automotive battery. Suggest you have it tested.
If the battery is OK then you should test whether it is being charged when
you drive and when you are plugged in to shore power.

Marve
 <><
'95 EVC