This is on your bus, right? With 6 layers of paint, how much rust can there be? Judging from your pictures it looks to be nice and solid, what has changed in the composition of that metal over the past 45 or so years that it won't hold paint anymore? Sorry, but I just don't buy into all the rust conversion/acid treatments. What primers are you planning on? Some of the epoxies out there have incompatibility issues with these acids, and not observing these issues may cause paint failure down the road. A properly media blasted surface is an ideal adhesion prep for epoxy primers without the need for rust conversion coatings.
Lastly, if you are
media blasting the body, large panels like found on your bus can be left a mess by someone who doesn't know what they are doing. Here is some reading on the subject, pay attention to Porchdog's replies, he does this stuff for a living...without inflicting damage.
http://www.trifive.com/forums/showthread.php?t=72038 http://www.trifive.com/forums/showthread.php?t=47896 He warns against using sand, as it is caustic and in many cases contains salt crystals in the mix....so once it gets to the bare surface the salt starts the rust process. If this doesn't get cleaned off, it will cause problems
under your paint.. He also doesn't use soda, as it presents adhesion issues just like the rust conversion acids. I'm certainly not here to tell you what to do or not to do, it's your vehicle. What I would suggest, however, is researching how each of your prospective steps will interact with the next, and what problems if any, that their use will present. Knowing all the info up front, you can make informed decisions on methods/products that are compatible throughout the process from start to finish.
