I've sand blasted small go-kart frames when I was a kid in my back yard using regular sand from a landscaping supply. Worked great, took only a few hours! However its still a lot smaller than a trailer frame. The sand had to be filtered as well to keep out all the big pieces so it wouldn't stop up the nozzle. For me it had to be an all day project so that I could get a rust inhibitor of some kind on the metal before it got dark. If you made it a weekend project though you shouldn't have a problem, the small amount of surface rust that you would get in a day or two could be taken off with some sand paper, which you will have to do some sanding either way if you want a good paint finish. Just make sure you put a coat of a rust inhibitor on it if your going to leave it for more than a few days. Just keep in mind that if your doing it "backyard style" like I did, your going to use a lot of sand, you could lay a huge tarp down and collect most of it and then reuse it but it will be contaminated with paint chips etc. I don't know if it will make a difference but it may stop up the nozzle.
Hope this helps!
O and also if you go this route, make sure you cover all bare skin because it will leave a nasty rash/burn.
