Personally I just spent all of May doing this and I did as much as I could with everything still together. I wire wheeled as much as I could possibly reach and then applied Ospho, an rust converting acid. When that was dry -about 24 hours- I applied Master Series Silver, a POR-like paint in that it cuts the material off from air and therefor rust. I bought them separately but the total was something like $120 for a gallon of the acid and three quarts of the Master Series, of which I used nearly all of the MS and maybe a quarter of the acid to do not just the frame but 8-% of the under-body too. -I couldn't really get to the tunnel and it was covered in enough oil and trans fluid to spare it for another day's project
oke:
Now, I do plan on doing the suspension sooner than later, so if I got paint on a bushing or dust cover, I didn't worry about it too much, I did try very hard to avoid the rubber with the wire wheel and acid though!
I tried to paint as much of the inside of my frame as possible too. Some parts were 'easy' if awkward and dirty, like the open channels in the middle of the frame, but on the boxed parts I did my best to get inside with an under-body paint gun, the kind with the flexible hose. I will say that the Master Series is very thick and the quality of this gun was very pore so it didn't so much spray the paint as burp it up in big splatters, but I tried to direct them into as much space as possible.
They do sell better under-body/frame painting guns, you can thin the MS ever so slightly, and or they do sell spray cans with a hose attachment just for frame painting, Eastwood most notably... But it is as much or more as finding a way to spray the MS or POR that you already bought for the rest of the under body... And then you have a tool you can use whenever you need it. But... I'm a big fan of buying the tools you need because I'm sick enough to imagine doing X project again in the future. :inlove:
Lastly, on the cheap, I have heard that transmission fluid has been used as a anti-rust coating many times before. It would easily be applied inside the frame rails with a pump sprayer, the 5 quarts of tranny fluid and bug sprayer probably wouldn't even cost $50 bucks all together and the nice thing about tranny fluid is that it is viscus enough to hang around for a while, certainly good enough to last until next year and repeat. -And it wicks to the dry spots... Meaning just because the sprayer didn't hit it doesn't mean you won't get a little protection there.
And again, it's cheep!
The only down side is that you ever do want to paint in there after, you'll really have a serious time trying to clean all that out so the paint will adhere.
Hope that helps a little, good luck! :beer:
Jeri~
