Rust on my 1988 Wrangler yj

I have some rust issues with my Jeep. The
interior tub is rusted pretty bad in some
spots. I recently removed the carpet and
found a nasty looking rust spot right where
my sport bar and my tub connect ( it’s in the
floor where backseat passengers stick their
feet). What is the part where the floor
connects to the sport bar called? How
should I go about fixing this( total
replacement because it causes structural
integrity? A nicely done sanding and touch
up with rust prevention paint?) I’m not sure
how deep the rust goes I don’t really know
how to determine that either. I really just need
some advice on what to do about it. Since I
don’t feel like I can fix it like I plan on fixing
the other rust spots( sanding or cutting out
the rust and welding new metal to the tub).
Any ideas or tips that you think could help
me out? Can get some pics in a few days
jeep is currently getting the clutch replaced.