Ulysses

Another vote for taking the body off. Once you dig into it you'll probably find a lot more rust and having the body and chassis separated will make it so much easier to work on.

By the way, if you want your repairs to last, cut out the old rot and replace rather than patching over it. If you patch over a hole, water gets in between the two panels and the repair rots out pretty quickly.

Sorry to see that rust has got hold so badly, your car gets more hours maintenance than most and still things catch you out.... Don't be disheartened mate, its fixable....

One other option could be to have a chat with Terry, he's got a truck cab in a container ready to go.... Told me £1500, I know it's a chunk of money but it is another choice if what you find is scary.... The shell is mint and has the square profile on the lower rear of the cab body to suit a full width pick up bed, he can supply them too if you fancy a change...

I can't weld now but I can cut, plate and form... if you want to hit it over a few days, I can come over and help..... 

sniper

Sniper that's a decent offer on both fronts. If it was me id go for one guy fabricating and the other welding, give the fabricator a head start and ye would be out of it in 2 days or it could turn into one almighty tea-drinking marathon and Jimny knowledge table quiz.  

Rough deal Riccy!

Chassis mount looks a little sorry for itself also......check the rest of the chassis too mate.

Rust is coming for all the Jimnys!!

But we can keep fighting Keithy

Gosh, that is bad! I didn't expect that on your Jimny at all given how often you throw the tools at it. Hope you manage to get it sorted. Document the process if you can! It would be very interesting to see how you do it