Boulder, CO to Salt Lake City, UT

I would do your option #1. Poudre Canyon is scenic, with lots of good campgrounds for a self-contained RV that doesn't need hookups. North Park is ah, lonely is probably the best adjective. Steamboat Springs, by contrast, is booming. After that, you could visit Dinosaur National Park, the Utah Field House museum in Vernal, Park City, etc., before you get to SLC. You might even want to take a short detour to incredibly scenic Flaming Gorge Reservoir and the Uinta Mountains.

If you need some camping ideas along US 40, see my blog HERE.