Fleetwood Coleman RV Batteries

[autumnal]

We just got our first pu. Bought a used, but excellent condition, 2001 Fleetwood Westlake. It has one 12 Volt deep cycle battery (non-gel). I would like to add a second (gel) one. A few questions:
1) There doesn't seem to be room on the tow apparatus for mounting more than one, so can I just put it in the front storage compartment?
2) How do I wire them both inline so that once the first battery is drained,

[dthurk]

If all you're looking to do is power lights, it might be easier to use separate battery powered lanterns.  If you want to use two larger 12 volt batteries, you may consider simply swapping them out when one is in need of recharging.  You can hook them together, in parallel if they're both 12 volt, but you would be using them both at the same time.  

I don't know if an isolator would give you the effect you're looking for.  I would suspect once one is in need of recharging and the other is brought online, the one needed recharging would drain down the second until both are at equal charges.  Others with more electrical knowledge than I will chime in here with more information.

[mike4947]

No real way of automatically switching batteries without spending upwards of several hundred dollars.You'll be better off using AGM batteries rather than Gel Cell.
But you will need to isolate them from each other. It's never a good idea to mix battery type in a single bank. Either get two AGMs or keep them seperate.
They will also have to be charged seperately if the type are different.
 
A few amperage draw ratings:
 
Single bulb, ranges from 1.4 to 1.8 amps per bulb. Two 2 bulb fixtures wil draw between 5.6 and 7.2 amps per hour.
 
Furances draw 3.4 amps per hour of fan run time.
 
Water pumps draw apx 5 amps when running, but the total amperage draw for emptying a 20 gallon tank with a 2.8 GPM pump is only apx 1 amp.