Holy Rust Batman! What to do?

Take a look at fluid film. A really nice product that is designed to be sprayed directly on rusted metal. I sprayed my fifth wheel several years ago and all well with no additional rust. I also spray my truck frame...local repair shop will do high pressure spray for about 120.00, or you can buy spray cans. It lasts longer on fifth wheels than tow vehicles as they don't see the same amount of road time

http://www.fluid-film.com/

My utility trailer had the same cancer under it. I wire brushed the loose stuff, pressure washed it, let it dry, and then brushed on KrudKutter's rust converter. It worked for the most part, but needed 2 coats as it went on like water as it's a really thin product. Once it dried I washed the trailer again to get rid of any excess that hadn't adhered/converted rust, then went through 8 cans of Rustoleum gloss black spraypaint.
Been a year now and still looks good, but there are some rust pocks coming back - trailer lives outside uncovered, so this was somewhat expected. I've heard good things about CorrosionX, so I plan to treat the belly with it come spring time. Good luck on your tedious project

http://corrosionx.com/corrosionx.html

My boat trailer had some rust issues from very limited salt water exposure. I used OSPHO on it and then bought some Rustoleum rust inhibitor, I used a wire wheel and brush got off all the loose paint and rust, then brushed on Ospho and let it sit over night (if any dampness out let it sit longer), Then sprayed the rustoleum rust inhibitor and then a final coat of Rust defender paint!!
Worked great!! And should do good on that rust!
Good luck!

it most likely sat at the manufactures lot in the grass then towed to ohio on our salted roads ,then sat at the dealers a long time. theres nothing safe from ohio salt.

Looks like it was driven on salt treated roads a lot...that IS a lot of rust for so new a rig.

Every spring with my fifth wheel. Wire wheel, Rust paint and POR-15. You just have to keep after each spring, looks like your's has been neglected for years. I just did some rust correction on my 2015.

If you keep after it, it becomes minimal each year.

Colorado ....no beaches nearby.

But it does look like some of the cars and trucks that I have seen that were regularly driven out on the sand on the WA and Oregon coast to the water's edge during low tide..

I'll definitely be doing some scraping.

When you figure the frames sit exposed to weather until they build the rig, then are often driven in winter time to the RV dealers, they've been exposed to snow and salt. My regular maintenance program includes Frame maintenance which entails scraping rust and repainting the frame on a regular basis.

Wow, that looks really bad. I think I'd be doing some serious poking around in the places you can't see very well. Who knows how bad it could be up where water/salt can collect.