if you keep the sandblasting in an angle to the surface and keep from staying in one spot will not warp the metal,the heat created from going straight on or staying in one spot too long is what causes warpage.and on the contrary about the sand in the nooks and crannies,it will absorb moisture and defeat the purpose of removing the rust.I use a full flowing air blower and a vacume cleaner and just keep moving around until it is clean,then do it again,and again it's time consuming but very worthwhile if done right.after you get it primed wait a few days and blow and vac some more then you can spray ospho in a garden sprayer into all the holes and edges and wipe it dry with paper towels.you could also use a sander and wirewheels to get all the paint and problem areas that you can with them and just sandblast the bad spots to minimize sanblast time.do your best to get the sand etc.out ! good luck