Easy as Will, not building one, you just bolt them together. Ive got 4 x 200ah Winstons in the van, and theyre only slightly bigger than the 105 lead acid they replaced.
See here
https://r.tapatalk.com/shareLink/topic?url=http%3A%2F%2Fwww%2Emyswag%2Eorg%2Findex%2Ephp%3Ftopic%3D43250%2E0&share_tid=43250&share_fid=54922&share_type=t&link_source=app
Cheers Glen