I am getting into the body work on my '80 f250. I bought a bed with some cracked, chipped, crap underliner on the bottom. I was going to sand blast that off. While I had the sand blaster out, I was thinking about blasting the inner fenders. Will sand warp, or ruin the metal on such a small surface? Ijust want to do the insides, because it will be a pain in the neck to sand them with all those wierd contours! Any help will be appreciated!

 

Course sand can cause problems with sheet metal.
I have been using soda to blast mine, it takes a little longer but it has no chance of damaging the metal.

 

Sandblasting can and will warp metal due to overheating. This mainly occurs on nearly flat panels such as tops, doors, hood. You should be fine.