I wasn't paying attention to this thread.
For media blasting, small guns like that will take a long time and you really don't want to use silica sand on body panels as the heat can warp them, especially large panels like the hood.....Not to mention the health hazard of blasting with silica sand.
The best thing to do would be to take it in and get it blasted for you. It's worth the few hundred $$$ to have it done by a shop that has the correct equipment to blast something large like that. They can do in a few hours what will take you weeks with a 1 qt gun.
You should use crushed walnut shell media or baking powder (or was it soda, hmmm, can't remember these days) on autobody work.
One of the reasons that the truck is rusty like it is, is because it was left in cheap primer and in the weather by somebody that probably started with good intentions and most primers are not waterproof. If you blast to bare metal get it in a good epoxy primer ASAP, even before starting to cut and weld in patch panels, epoxy primer is waterproof.
Body work can be done after the primer is on. You'll just have that small area you are working on exposed to the air vs the whole truck.
Patch panels don't need to be welded solid, a tack every 1" is fine. I have a pneumatic flanging and punching tool I bought about 20 years ago. Saves time and makes for a nice repair when the patch you put on sits flush with the rest of the body and the punch lets you put in spot welds that look like the factory did it.
Good luck