Removable rear seat conversion

This section is a project in itself!
when I got the van I wanted to take out the seats but after a while I found it so useful to be able to carry 5 extra people around that I started thinking of a way of making them removable.
The main stabling block is how they are fitted.
they are factory fitted seats which bolt through the chassis with 9 hefty bolts. unfortunately all of these bolts are completely inaccessible from underneath with out first removing the fuel tank and the exhaust pipe!

The eventual plan is to weld the nuts to a piece of 'U-section steel and bolt that permanently to the underside of the chassis so that the bolts simply drop in from the top and tighten with a spanner and I won't ever need access to the under side again!
This is more tricky that it sounds a slightly beyond my expertise. But my mechanic friend paul has offered to help me with this so it should be easy!

I will post pics up when this is under way!

UPDATE: ok so I got round to having a look at the rear seats. Got under the van and dropped the fuel tank and exhaust and managed to remove the rear seats. This took a whole weekend and there was only 9 bolts! The bolts were so corroded that some of them simply sheared off when I tried to remove them. I settled for simply replacing the tank and living with no rear seats for now. Still got them for the project to resurface at some point. We'll see. At least I can fit the bed now!