Optima is good if you only want 44 amp hours..... But I went this rout. 
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AUXILIARY Battery setup: I've installed the UB12220 batteries in groups of four. This is the maximum amp/hour storage battery I've been able to fit into a stock Vanagon battery box without modification. Each UB12220 stores 22 a/h, totaling 88 a/h for a group of four. By comparison, the Optima yellow-top is only 55-65 a/h and requires cutting and other modifications to make it fit. The little Odyssey PC1200, stores 44 a/h. As you can see, the UB12220 package offers the most storage capacity for the space. Fabrication of simple bus-bars (using 3/4" aluminum angle) is necessary to tie these batteries together, but it makes a tidy package! 
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Here is the link. I am going to add 10 more of these battery's in the bottom of my rear closet then cover them with a board to make for a new bottom to the closet. The closet is so deep and I never use all the space. I also have a 1500 watt inverter and can sleep and run my electric blanket for 6 hours on the 88 amp hours.......
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http://www.westyventures.com/parts.html

Danny 
'84 Westy (Vanny)
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--- On Tue, 6/30/09, John Rodgers <inua@CHARTER.NET> wrote:

From: John Rodgers <inua@CHARTER.NET>
Subject: Optima Batteries vs Others
To: vanagon@GERRY.VANAGON.COM
Date: Tuesday, June 30, 2009, 6:45 AM

Looks like I may have a battery purchase coming up and I was wondering
about what battery would be best. I have thought about an Optima battery
but really know little about them.

What say the list on the Optima and which would be recommended?

I drive an 88 GL.

Thanks.

John Rodgers
88 GL Driver
Chelsea, AL