Hi Gordon
One of the problems you have with the Berlingo/Partner van is the position of the fuel tank underneath the van.
My experience is fitting a 500litre upright tank into my son's 800kg Partner HDI.
If I was doing this again I would fabricate a frame that would fit over the tank - like a box without the base if this describes it better. This would allow the tank to sit directly on the van floor. The base of this frame would be of 50mm angle iron welded into a rectangle to fit snugly around the base of the tank with the frame welded to this base. I would weld lugs onto the transverse sections of the base. The lugs don't have to be very long at all, but need to be long enough to the front to be secured through the plate that covers the rear passenger foot-well (if you had a rear seat) with 150mm flat plates to spread the load (we used 25mm x 5mm flat bar.) The back lugs would be slightly longer. On my son's van we drilled the rear holes 250mm to the front of the 'ridge' that is clearly visible around about the rear axle position. This allows us to use 200mm flat plates accessible from underneath the van. The holes in this plate were drilled offset.
As the tank is not positioned exactly across the centre of the van the rear lug holes are drilled 370mm from the nearside wheel arch and 420mm from the offside wheel arch.
This way we didn't have to remove the tank. Please don't be tempted to drill holes through the floor above the tank to fit those 'blind' rivet nuts (can't remember exactly what they are called.) I know about a Ply-liner who had the replace 100 Berlingo tanks because he used screws that were too long to secure the ply floor to the floor of the vans and all their tanks leaked diesel when filled up.
I would also recommend a factory fit half bulk head which is very strong and gives added protection to driver and passenger.
In our case the Partner is very small and we had to provide a channel (used roof gutter section) to store his Unger poles in the van. We cut a small section of the bulkhead out so the poles would extend into the cab between the door arm rest and the storage compartment and sits on the nearside wheel arch. Unfortunately if both of us use his van he has to open the back first and remove the poles so I can get in/out - Health and Safety would have a field day with this but he refused point blank to fit a roof rack and pole carrier.
We fitted an 85ah leisure battery under the fold-up passenger seat. It sits in a stainless steel baking tray purchased at Morrison’s. He also has a split relay charger fitted to the van - but as we are only local we boost charge the battery once a week just to be sure. If he is caught with a flat battery, he also has a change over switch that will draw current from the van's battery.
I put pictures on the site in the middle of August.
www.cleanitup.co.uk/smf/index.php?topic=41726.0Hope this helps
Spruce