what to do on inside of the body panels in trunk area?

[Lord Warlock]

Last weekend, i dropped the gas tank, and cut the rusty floor out of the trunk, its mostly just the center section although there is some rot in the floor behind the drivers side wheelhousing, i still have to cut that out too.  While i was sitting on the floor, with my waist up sticking thru the new hole in the trunk, and cleaning off the rear differential from decades of mud/dirt crust, I happened to look upward and noticed that the insides of the sail panel, and the upper portions of both rear fenders are showing surface rust, not heavy rust where its eating through the panel, but enough where If i left it alone, it would eventually eat the good metal from the inside out.  I can't realistically get a wire wheel grinder up there to get most of it off, and don't have a sandblaster to do the job inside where it needs to be done.  What do people do with those areas?  I know that we can use POR15 paint to seal it off from the air and contain the rust, using a spray can of something would be a lot easier to get some of the tight crevices of the upper rear fender near the roofline above the wheel, but really haven't used any of the spray on rust inhibitors  before.  I've used POR15 before but wouldn't want to spray that stuff through a gun, its pretty much a brush or nothing with Por15.  Also can't be careful not to get drips when doing some of these areas, and getting por15 off the skin is troublesome if it gets on you.  

The inner sides of the panels were covered in factory undercoating which did a great job of keeping the rust out of these surfaces on the inside,  but the tops or ceilings per se were left bare, and the rust is collecting moisture in the air.  I almost never get in a position that i could see it, but had a 1000 watt halogen shining up from the floor inside the trunk area, and i could see moisture on the inside of the trunk area where it was rusted inside. I can't just let it ride, I have to do something now that i know its there.  The top of the right side rear fender is already so thin that it doesn't support leaning on it without  flexing.  I'd like to treat it to keep rust from getting worse, then i could use undercoating bed liner or some other product to cover it up.  These are areas that probably never got painted from the factory.

[sanders7981]

One of two things come to mind... Bed liner, or some of the undercoating with rust preventative chemicals in it.  I think most major brands have some type undercoating like that now.. East wood, 3m, rustoleum  to name a few.

[Lord Warlock]

i ended up getting Por15 Prep and Ready, which is clear but is supposed to neutralize it and coat it with a zinc coating of some sort, then took some rustoleum rust treatment and sprayed it over the same areas, especially as far up front of the rear wheels as i could reach, the inner side of the right rear, the one with my biggest concern i coated with por15 sealer, the drivers side with the filler tube hole didn't show any rust So just treated with the Prep and Ready and rustoleum.  Under the package tray, the worst looking of all got all three.  Once the Por15 has time to set up, and after i do the trunk floor welding then I'll have to treat it all with por15 and topcoat it. 

Heed the warnings on por15, its hard to get off the skin, thank goodness for brillo pads, got most of it off.  Hope the glad wrap under the can lid will let me keep it fresh for a while, it isn't cheap paint.

[sanders7981]

POR 15 has some good products, pricy too, but preparation is key and it works.