Jason, the Optima D750U or D750 will fit if mounted on its side.

To be able to slide the battery into the Vanagon, you must first remove the
metal mounting bracket. Install the battery with the +ve and -ve posts
facing toward the front of the van so that they protrude into the opening
under the seat. Use a strap to hold the battery securely.

Larry

Jason Yasment wrote:

> List,
>    Here is some info I received from Optima battery concearning starting
> and deep cycle batteries for our beloved vanagons.
>
> The battery that fits your camper is a group 41  11 9/16 L  X  6 7/8 W
> X 6 7/8 H.
>
> The Optima is a group 34  10 1/4 H  X 6 13/16  L   X  7 7/8 H.
> The only problem I see is the height, if you have clearance it should go
> right in, you may have to modify somewhat.
>
> For starting I would an 800U and for the deep cycle I would use the
> D750U.