There's a very simple answer to fitting a tank in an electric van, and its literally looking you in the face. It applies equally to any petrol or diesel van too. It would be possible for anyone able to use a few spanners etc. to fit one perfectly safely in a vehicle.
Here is the cargo space of a typical van. There is no need to drill holes to secure a tank. The holes are already drilled and fitted with 'lashing points'. The lashing points are rated to hold (in total) the payload. In this example there are 6. As i think of it, most vans have 6 anyway wether its a Berlingo or a Boxer. Typical set up :

What everyone has done for years is ignore them lashing points and drill your own new holes exactly where your tank frame is and where you want it to go . So it looks something like this..... (red is the frame and green is the new drilled holes):

If the frame was made to fit the vehicle then you would be able to remove the lashing eye and bolt, place your frame over it and bolt your frame into the existing floor nut. There are numerous ways to adapt a frame, spreader plate pre drilled etc. But it would probably mean that your frame would only ever fit that vehicle. I.e a tank frame for a vivaro would not fit in a Ford custom etc... But thats no different than roof racks. It just means buying a frame that fits your own vehicle and utilises its existing lashing points.
I'm having fun with my green and red pen!! :

Someone should of got onto this before me, i'm not the sharpest tool in the box !!

I didn't mean to hijack this thread into a tank fitting one, but seeing as the fitting of a tank into an electric vehicle using old fashioned methods is a very difficult and costly method. And seeing as Soupy even had a custom made spec frame and still drilled through his floor i still think people are missing the very obvious, although a few of you have touched on this subject in this thread before.
Not mentioned that i can see is the price for the fitting of the tank, how much was it Vin?
Vin .