.Some people have told me to just hit it with a coat of primer/paint but wanted a second opinion.
Glad to have you with us on the forum! These trucks are great to learn on, and this is a great spot to do research. That being said,
Anyone who told you just to hit it with a coat of paint is dead wrong. I repeat, dead wrong, they don't know what they're talking about. When you paint over rust, all you do is hide it. Rust is cancer-- it must be excised with extreme prejudice. Also like cancer, there are different treatment options depending on the severity of your frame rust.
Stage 1: Light surface rust, no pitting or flaking.
This is the easiest rust to treat. You just give it a little love with some abrasives, like a wire wheel, wire brush, or even rough sandpaper. The goal is to get the rust off the surface, then wipe clean with methyl hydrate (to prevent flash rusting from using water to rinse the metal clean). After that, prime and paint with rustoleum, tremclad, or if you're overly cautious, POR 15.
Stage 2: pitting, flaking or light scale rust.
We're getting into the more difficult rust to treat, here. You'll want to attack the rust with a hammer and cold chisel (not a chilly chisel, it's a specific type) to break off any lumps of scale. Focus on the big lumps, if you can smack it off, it has to go. Even just whacking the frame with a hammer can help dislodge chunks of rust scale from the vibrations.
Keep your eye out for more serious rust spots, anywhere where water is retained, on the lower part of the 'C' channel. Once you think the lumps are gone, repeat the rust treatment steps from Stage 1. Go over it as many times as necessary to remove all the rust. Then, wipe clean and paint.
Stage 3: Large, flaky scale, heavy pitting, and significant rust accumulation.
Ok, at this stage we need to involve some power tools. Namely, an air chisel and a needle scaler. These tools will dislodge the large flakes, blow the rust chunks off, and eat their way through to the clean metal hidden underneath (hopefully). Vigorous removal of the scale, followed by a grinding with a wire wheel, will get you close to where you need to be.
Then, when you're close, get a set of safety goggles, some rubber gloves, and muriatic acid. You'll want to give your frame an acid bath, brushing the acid on with a cheap paintbrush. Don't get it on your skin, it will burn. The acid will etch it's way into any remaining rust on the frame, allowing you to assess any areas that may need more descaling. Repeat this process as necessary. Then, when you're satisfied, rinse the frame down thoroughly to neutralize the acid and follow the rinse immediately with the methyl hydrate wipe-down. Paint and enjoy.
Stage 4: the rust is terminal, time for a frame swap or major repairs and patch welds to delay the inevitable. I'm going to assume that at 15 and with your budget constraints this level of work is beyond what your are able and willing to take on.
Hope this gives you some assessment criteria for your frame, so you can figure out how involved the rust fixing needs to be!
