i have an 03 montero limited and recently I've noticed rust on the passenger side inside the hood going through to the other side (front passenger wheel well)

its kind of at a hard place to reach, any ideas on what i should do?

 

here are the pictures

i have began to sand them down, but the further i go, the more rust i find

any suggestions how i can fix this for good?

 

swap out the quarter panels.
Only other alternatives are cut and welding or bog.