Cab floor rust: what are my options?

[In The Ten Ring]

This truck's previous owner, my dad, had it bondo'ed and painted back in 1990......they skipped over this hole!

I'm thinking about riveting in a patch and undercoating beneath, getting me by until I hire a (real) "body shop" to fix it right. It's in a bad spot though as it is "L" shaped.... and the rust area includes all of the surrounding brown-tinted metal.

I had planned on driving it as is, and getting this fixed later, when I have some cash saved up.

What do you guys think are my options?