what do you think of rustop undercoating.my 04 f150 starting to show signs of rust around cab corners and such .thanks

 

eh, it's my understanding that the time to apply rust-proofing is before the rust starts. Suggest you will have to clean all the current rust before applying - and then the questions of how well the rust was removed will remain. Further suggest that applying rust-proofing over material already rusted will only accelerate the problem - perhaps mask it for a bit longer - but the rust will eventually show up bigger and badder than if left alone.

No personal experience - just speculating.

 

Rustproofing is ideally done when the vehicle is new. At this point, the idea would be to remove the existing rust and protect it from spreading. There are many after-market products for removing and protecting from rust. Good luck!

 

Look at Eastwood company web site for products that stop rust before you go any further. I have used one on an old vehicle and it does work.
Also you may want to talk to zebart.