Repair-It

Treating the floorboard rust while the exhaust is off.

Some before shots of the driver's side: I used a wire brush to remove the loose rust and an abrasive pad to clean it up areas I couldn't reach with the wire brush. After that I used Chassis Clean to clean various oil debris and rust dust of the metal. It seems to be a lot like brake cleaner.

After two coats of Rust Encapsulator: Next step: Chassis Black. More pics to follow.

Cleaned the passenger's side and applied two coats of rust encapsulator. I've used 3 cans so far,

No more pics yet. However, the passenger side has less rust than the driver's side. So there's that.

Is it time for me to order that stuff yet? I actually should deal with both the Roadmaster and Ram.

Probably.

Those cylinder brushes are great for doing the frame and getting large flat spots. You will want something smaller to get in the tight areas. Also, maybe a chisel or something to help get the loose rust off.

If you are doing multiple cars, you may want to see if you can get case discounts on the chemicals.

Pics from after two coats of Chassis Black. Sorry about the lighting, it was daytime outside.
If I was a perfectionist, I would have used a flap disk or other grinder to take it down to smooth bare metal before painting, but I'm not.

The orange in the top of the last photo is the reflection of my gloves. It is fairly shiny under there, now.

Could also look at Rust Cap by Hammerite.