Exactly how big of a deal is rust on my frame...

sandblast if possible when painting with por-15 or chassis saver brush on 2 coats the 2nd coat is the real difference maker

 

You can wire wheel it then put vinegar in a spray bottle and spray it on. It will clean the rust right out of the pitts and let you see the damage.

 

If you use a product like Line-X it actually will do a better job then POR15 if you sandblast the frame down to bare metal prior to the Line-X application. I had a long talk with the guy at a line-x dealer about this. Plus the fact that the stuff is guaranteed for life not to chip, crack, peel, and fade is an added perk!

 

If the OP decides to go the POR 15 route, find a good automotive paint supply product store and get everything you need. Like said above get a good acetone, or a liquid metal etch and after you sandblast or wire wheel the area spray it down the degrease and paint on the POR15. I have done tones of stuff with POR15 and I have had AWESOME results on my pickup truck which is also my plow truck up here in Chicago. You can get different colors and gloss or semi gloss finishes.

 

Not sure where my pics are but I can tell you how tuff that stuff really is if you apply it thick enough. Friend of mine did a Resto on an old late 60s pickup. Coated the whole frame in POR15 and did about 5 heavy coats of it. Something broke on the truck and the place he was buying the part from needed the VIN off of the frame. Well the POR15 covered it up and you could not see it so he ended up using a stack of masking tape around where the VIN was and poured brake fluid in that rectangle of tape and let it sit for 3 days..... After the 3 days he cleaned off the brake fluid and could read the VIN but there was still a good coating of the POR15 left on the frame. Everybody knows, brake fluid eats through paint like its nothing. Good stuff in my book and cheaper then Line-X and I get a sense of satisfaction in doing things my self which is why I opted to POR15 the floor of my pickup instead of bringing it to Line-X.

 

I just dug a left over pint out of my basement (POR15) --It says it works well right over rusted metal (I would still wire brush it then wash or use blower to clean dust) --it doesn't want you to use any rust converters underneath and to be careful not to use any degrease rs that may leave a film. (clean with lacquer thinner after, if you do degrease first). I see nothing about needing any primer first but if you apply POR then want to paint over --you need to use "Their" etcher.
FYI: POR was about $25.00 a pint last time i bought it -and a pint goes a long way.

 

Oh don't worry about it, I've got a 15 year old truck that I drive that never got a wash in its life, the frame and deck are both a little rusty but there is no pitting nor is there any issues with the frame.

 

Is there anything that comes in a spray can?

I have always kept spray cans of rust-o-leam on the truck and sprayed things while waiting a round for loads or a break.