There's no "miracle" body filler that goes on that much better. They all have to be mixed correctly, and then sanded down to match body lines and contours. A great one for filling in rusty areas is called all-metal. It's made of aluminum shavings I believe. It cuts down on the chance of the rust coming back. It is kind of difficult to sand correctly, though. That rust convertor stuff looks okay, and then there is POR-15 also, which is a little more expensive. Both are decent for inner body panels on rusty areas. I've found most of those types of products don't sand well for top coating, ie: primer, base, and clearcoat. Do you have any pics of the bad areas?? You might be better off having someone migweld in some patches for you. This is usually the "best" way to repair rusted body panels. You can also get the areas sandblasted and use some long strand fiberglass filler if welding is too expensive. You fill the rust holes with this, sand it down, then use the bondo type filler on top of that to smooth out the body panel. Here is a page with some of the common body fillers and there typical uses. Good luck with the repairs, body repair is a learn by doing process.,,,,,98
http://www.crestnetsales.com/body.htm