Wow.. 300 just for sandblasting... must be the government doing it...
my body man charges me 50-75 for all the blasting on a standard 81 or similiar... Hope he is not reading this...
when i used to get the inside tanks zinc plated we ran into the "Trapped" acid situation a couple times.. would have to take them back and redo, and not always was it remedied.. hence got away from the zinc..