Newbie here guys...but I ran across this and couldn't resist from writing from my personal knowledge. The "bubbles" you may see in coating is commonly referred to as "outgassing" of the metal. It's alot to explain the process at which it occurs...but how to cure that is easily done by baking ANY aluminum after sandblasting around 425-450* for about 15 minutes or longer, depending on the thickness of the aluminum. I try to outgas iron too that has been exposed to oil and gas in it's lifetime.
Another thing you guys wanna try is using this stuff called iron phosphate. You can order it from columbia coatings. You just dilute it in de-ionized water, or buy some water from the store that is mineral free. Rinse the part in that solution for about 2-3 minutes, then rinse with the deionized water. Stick it in the oven to get it dry and a little warm, then shoot the powder to it. The powder sticks really well after prepping it this way. I use to hit my sample panels with a ball peen hammer and the powder never chipped or flaked off. Also stuck the banged up sample panel outside in the exposed elements for months with zero rust issues.
I have powder coated on my own for several years and use to do it commercially for a business in Florida, so I am pretty solid on my advice. Make sure all the previous coating is stripped off completely, then sandblast after that for a good "etch" on the metal to offer better adhesion.
I just bought an 02' blaster and am going to tear it down thru the winter months and powder coat everything. I will be sure to post up some pics of my progress as well.
Hope this knowledge helps! If you guys need some links to buy good reputable powder, let me know!
I also built my own 6' powder coating oven to do frames...but it is currently disassembled due to moving. It will be back up though soon to start on this Blaster!