With the idea of purchasing a new transit, I'm curious as to whether there may be an alternative procedure that enable the tank and frame to be secured, but doesn't involve drilling through the vans floor.
Are there any other options?
Yes, fabricate an appropriate size of flat bar to bolt from the tank frame through the pre existing holes in the van door pillars, and if you want to go the extra mile do the same again to bolt into the rear and/or side pillars (depending upon what van you have).
There are lots of ways to secure a tank in a van, and make it stronger than anything that currently exists on the market. Its a simple affair to extend the tank frame to reach all the pillars, these extensions could be incorporated into some sort of pole racking affair etc..
All the market leaders seem to favour a bolt through the floor option,thats because its a one size fits all scenario and suits them best (not neccesarily the customers needs). Custom fitting requires a bit more thought but results in a lot safer securing system. It would also be very costly to get accreditation for every vehicle permutation, thats why its not done i imagine.
As an aside, i hope i'm not taking your post too far off topic, i have come across vehicle insurers who are now insisting they will only insure fitted tanks that have been installed by how can i say it? The leading manufacturers fitters, i.e Ionics, Brodex, Grippa etc.
Nice to see their concern for our safety extends to ensuring we can only be insured by using one of them and their old hat techniques of bolting through the floor. Perish the thought of them investigating baffling techniques !!! The only technique thats baffling me is how they are persuading the insurance market to require them to be used :-)