Having spent inordinate time researching how to rustproof the inside of a fully boxed frame, I decided to do a more temporary job of just spraying it with oil. So far I've sprayed the inside with warm degreaser, followed by a thorough rinse, now it's drying. I thought the inside of the frame would just be dirty, but it's actually as rusty as the outside. Should I head straight to spraying oil like I set out to do, or is it going to come back to haunt me if I don't clean up the rust somehow? It's hard to get in there; will just spraying inside with phosphoric acid do the job?
The inside looks like this outside: