Best way to seal bare metal BEHIND patches???
 

I've heard of weld through primer but the welds will still be exposed to the elements. My question is this... Once you've made a rust repair in a place that cannot be accessed from behind, how can it be sealed or treated to prevent rust from forming from behind?

Thanks

on most things you can get to the back side of a panel with cavity wax and the 4 foot wand on the gun thats made for it . the wand is very small and will fit up in side things like rocker drain holes . most panels do offer some kind of a little hole to get a wand in .

Perfect! Just the thing I was looking for.

Anybody use the aerosol can for this... I have only a few small areas to protect, the gun seems overkill for a tool I will likely use only once. Also, is this something that will need to be done intermittently as part of routine maint.?
Thanks again

you can get spray can with thows red tips like wd-40 has . if that will reach to were you need to get .