Hi, from experience, and I am a bit old fashion on this topic, with several older cars I have found the following. If is it significant (holed teh panel) you need to treat rust like cancer - if in doubt cut it out!
Other wise the following option might be useful.
-wire wheel on a 4in grinder isn't bad for flaky surface rust but it pays to treat with deoxidene after;
-plain old solder works well but need to be careful of heat (very useful in around window apertures, etc. Some guys also use nickel bronze but this is more limiting due to heat - but a good option in some structural areas;
-deoxidene (phosphorous acid) works well on light surface rusted panels;
Resist filling rusted areas with bog.
After you have dealth with the rust, by far the best option i have found to protect ext panels is 2k epoxy primer. You do need to apply to bare metal. It doesn't seem to allow the rust to creep under the paint even when chipped back to the bare metal.
Internal channels, sills, sections, crevices between panels, etc -clean thoroughly and then apply a penetrating rust proofing product. I thin and heat the product before applying - just to be sure. Suggest going to a specialist automotive paint place. Smells a bit initially but that soon goes.
Well those options have worked for me in the past.
Hope this helps.
Ian