Tape off every screw hole . You will not believe how much sand gets in the car and very hard to get out.
Back in the 80's I sand blasted a Duster shell and blew it out real good with air. I then sold the car due to my fathers death and I bought it back in 2010 and put it on a rotisserie.
When turning the car on the rotisserie you would not believe how much sand was still in the car and came out. We turned it and blew it out for a whole day and got at least a half a bucket out of it. In the rockers , cowl, roof braces, everywhere. Just a heads up. I still sand blast the rust on many cars but only what is needed. Use crushed glass not sand less warpage and coarseness is done to the metal. Also blows out easier
If you ever blast in the evening the blaster looks like your torching the metal off with sand.