All very good ideas. Also Bad Lucks rust isnt too bad
First thing to do is to descale the entire underside as much as you can.
You can loose about half the steel thickness and still be mosty structural sound. If the rust takes 3/4 of the thinkness of original steel. It needs replace d
This descale process will show you if your rotted through. Any questionable spots test with a hammer to make sure.
Once that's done. Clean the steel as good as you can.
Then coat the entire underside with corroseal 2 heavy coats. Its non toxic and is an excellent primer.
This can take the place of por15 or kbs seal. If you dont wish to use those products.
I actually quit using por 15 for its cousin kbs seal as its a newer formulation then POR 15 and less expensive.
I did a complete frame in por 15/ kbs seal and in some places it rusted again. Which was most likely my fault but wasnt happy at all. As the rig never left my garage yet
From my experiences. The paints [ including por15 and kbs seal] are indicators.
The corroseal is a rust inhibitor if you descale the frame and dont use acetone to degrease the frame. You can coat everything with it.
After that's dry you can paint the undercarriage with whatever strikes your fancy. I mostly use rust oliem as like I said paint is only an indicator. Then coat Everything with your favorite liquid rust inhibitor fluid.
All the doors, inner rockers fenders with this liquid rust inhibitor.
Clean the inside of frame of all the debris as best you can. Then go crazy with extremely heavy coating of your favorite liquid rust inhibitor.
For me my favorite is Fluid film. However it will not stay in wheel wells because it washes away from the power washing effect of the tires. So something else like cosmoline would be better in the wheel wells areas.
If you have rot holes in the frame. Then you have to cut the rot out and replace it. All kinds of ways to do that on my build thread. I perfer the inner frameplating as it eliminates the frame factory holes and gives you steel to weld to if brackets need replaced etc. It also keeps the frame the same dimension [ excluding the bottom rail] and just does a better job in the long run. Once your factory holes are gone when you coat the inside of the frame it cant rot out again ever.
This is just how I do it. From my experience of living in the rust belt all my life.
Sent from my SM-J337V using Tapatalk