Assuming you're talking about the free-standing, red tank kind of outdoor unit, I used one to blast a large machine. The issue you should be most concerned about is not the sandblaster, but the compressor you have to run it. I was using a pretty ordinary 5 hp, 2 cylinder single stage compressor and the sand blaster would **** it dry in a minute or so. So, you wait for it to come back up and have another go. It worked, but it took a long time. It hindsight, I'm not sure that a big gnarly knotted wire brush wouldn't have been faster/less annoying for a lot of the project. If you do decide to use one, be sure to open the valve all the way as it says in the instructions. If you don't, the rushing sand will cut through the side of the valve in short order. I was trying to throttle things to use less air. Didn't work out too well.
AFA how would I do what you want to do. Take the truck bed to a professional blasting place. Pay the money and move on. Undercoating that's attached does not sand blast all that well. The loose stuff with rust under it will blow right off.
but yeah just saw they were running a special so I picked up the 20 lb for 40 bucks, I’ll be transferring all my nozzles and hoses from my old blaster to this one and I’ll only be using dry play sand!