Paint for Frame, Underside, and Firewall.

I have a 67 CA car that has some surface rust on the under side of the body and frame but nothing serious. I was going to take a wire wheel to frame, underside, and firewall and then spray with something to protect it. I have been looking at the Eastwood Rust Encapsulator Black Aerosol and then going over it with some Eastwood Chassis Black Satin Aerosol.

I'm not married to these they just look like the simplest to work with and im working out of my garage and have limited resources.

I'm only looking for something simple that will hopefully make it last awhile longer.

Any input would help. Thanks!