I have a home made Westfalia, to which I 'd like to add a deep cycle battery (s) to run a Coleman Cooler I just bought and some other stuff including a laptop and some lights. Maybe even a v. small electric heater. I'm not planning to put the battery under the driver's seat but behind the passenger seat in a box which will have the cooler on top of it - box to be relatively open with ventilation to the interior of the van.

I've seen a kit on Bus Depot for $19 US that includes a fused relay, wiring and instructions. 

Has anyone had any experience with this setup? Is the stuff good quality and does it work properly? Is this the best way to do a deep cycle solution? Could I get all the stuff in a Canadian auto parts store as cheaply with equal quality and not have to pay the shipping?

Any practical advice/experience would be appreciated.

I've also had people warn me about venting the battery (s) to the outside or perhaps run the risk of explosion after charging from production of hydrogen gas. But I understand that the deep cycle batteries were situated under the drivers seat for decades of Westfalia's without trouble. Anybody got any expert knowledge/experience about this safety issue?

I don't know a lot about automotive electricity so please keep any advice simple..

Alan Pickersgill
Ottawa Canada 
85 Transporter converted to Westfalia