I used a similar product to do all of my interior frame, panels rockers front skirting inner doors etc. Mine was from Napa and I purchased a special gun that as several tube/nozzle combinations. Mine is a waxed based product that continually creeps and penetrates. Only negative is smells sweet when first applied so expect visits from your local wasp and bee communities. After a couple of weeks the smell goes away. Cleans up nice with mineral spirits if you get it on the paint. $200 for the air gun and $40 for a gallon of the product. Those are Canadian prices so probably half in US funds. Same stuff that is used on my VW.
I've used te oil/wax stuff, but I haven't seen the paint/convertor stuff before. Maybe next time I'll use the Eastwood stuff and then the wax stuff. From what I've found, the insides of out frame rails, seat rails , etc are only painted on the outside from the factory and the inside is bare metal, (well, for a little while, then it's rusty metal).