I'm not sure about the sealing process they did because I can't see what chemicals but it looks like a well done job. Completely remove the rust, patched in a new piece, welded, maybe sealed and primered, painted and very well-covered against overspray. Good job.
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Rob.
Current:
2001 E350 PSD w/ a bunch of stuff.
And had three other E350s...
I agree with most here that if you live in a coastal area especially, then you have to keep an eye on that roof. I have tried rhino liner and all sorts of paints on my repairs and have found that the most robust solution so far has been repairs with bondo an/or fiberglass then a generous coating of flex seal. The flex seal is extremely tough and provides a nice buffer to the rubbing of the pop top gasket. I also put a light coat of silicone grease on that pop top gasket to provide a bit of lubrication between the flex sealed areas and the top. The flex seal has lasted longer than anything else I have tried and seems to stop rust dead. Eliminate moisture and oxygen and you will slow the rust significantly.
I know there are way more solid fixes, but I feel like automotive paint does not stand up to the rubbing and the roof tape traps moisture. For a DIY solution I am very happy with it.
Reviving this thread again as I am staring down the exact repair right as snow is piling up in the hills! When they welded in the patch what did they do to protect the top and the inside of the van from fire? It looks like the top was not removed but appears there is a fire blanket used. My inspection today came with the immediate recommendation to have the top removed before welding to prevent a fire. I thought about stuffing the cavity with insulation that is fire proof. Anyone have thoughts on this?