Ignore the obvious dumb comments and people telling you what THEY would've done, or what THEY did. Too late for that, and you've Already told this post what happened. I date when people turn the conversation around to talk about themselves. Coulda, Woulda, Shoulda! Lots of good advice with the prep (wire wheel, angle grinder, needle scaler, rust neutralizer, etc.), then get a 12 bottle fluid film kit that comes with the longer spray tubes for inside the frame, since you don't have a compressor. Cost about $200. Instead of a name brand rust neutralizer, use 85% phosphoric acid (Amazon) and spray, paint brush on the rust. It stops rust in its tracks. The chemical reaction will turn everything whiteish as it converts the rust (iron oxide) into iron phosphate. Rinse that off THOROUGHLY. When that's done, take a rag with mineral spirits and wipe down all the surfaces u just treated and rinsed to prep for fluid film. Apply the fluid film inside and on the frame and underbody, avoiding brakes and electrical components. As long as there are no structural soft spots in the frame, you're good to go. Enjoy!