Thanks Dan for answering my question.
Yes, I understand you not wanting to do a complete body prep and paint if the climate you are in causes the body to continually rust. Florida is also not so good either but I looked very hard for the 2 I have that were very rust free. You have to pay more for the better ones also.
I will give you a couple of products I use to prevent the rust from coming back on a proper patch work. Ospho is a liquid metal prep used after you have done your patch repair( Welded In Patch). Then I use POR 50 this is a black sealant coating that is used to prevent moisture from getting back into the area to start the rust process again. I showed a pic of the firewall repair the black color was the POR 50.
The POR 50 is a bit of a PITA to use though. Once you open the can you really need to use it all at one time. Don't get any on your skin ( Use Gloves ) and you will have to throw away any brushes used. I prefer to get the small I believe it is a 3 ounce can then there is not that big of a problem using it up.
I can’t take credit for the paint. I paid to have this one painted. Just had too much to do with the mods, engine rebuilding, machining up new parts, new inlet and everything that was old or damaged to take that on too.
I can how ever answer some of your questions becuase I do body work when it is needed.
The gray color is a primer sealer. This is used after repair work is done and for sealing the old paint in so it doesn't bleed through your new paint.
The Fogged in color which is just some cheap black paint. This is used to see any low spots when you use a long board to sand the body with. If you are getting a ruff surface you will need to step down your sanding grits until it is better. It is better to use the long board which spreads the sanding in a much larger area and you will be able to do a much better job on the body work.
These disks you were ref to are not the best to use they are just too small of a surface to read the body work. If you are very experienced with body work you may get away with it.. You could pickup a book on body repair for beginners they are very helpful. I have found the materials are very expensive particularly the sand paper. This is another reason I decided to let someone else do it.
Terry
Ospho and POR 50 used on this repair
Here is a Link to the Sanding Boards
http://dura-block.com/durablockline.html 
That will be a real hand full. The bikes I use to build with the Chevy motors did 9.6 sec in the quarter mile and that was a hand full at only 360HP.
I was only joking, I would never expect you to let some guy from the UK drive that beast, Not even sure I would be able to handle it at full throttle, I think the quickest car I've driven was only around 300bhp so not even half what that has 
