We are here right now with a 39’ motorhome plus a 22’ flat bed trailer. We fit with a little tight turn just before camp site 23 where we are located. There is a sign just before the entrance that says no vehicles over 40’, so I wouldn’t recommend it. If there are any vehicles close to the road in a campsite, you’ll scrape them.

I think 43 would be too big for Castle Rock, however, the nearby (also associated with Fremont Indian State Park) the road Sam Stowe Campground is perfect for big rigs. It has 7 full hookup sites: https://www.campendium.com/sam-stowe-campground-fremont-indian-sp

I think it would be tight, but the official website does show a few sites that can accommodate up to 45'. The road in from I-70 is fine, it's just a matter of getting your trailer and truck into the site. Here's the link with site details: https://utahstateparks.reserveamerica.com/camping/fremont-indian-state-park/r/campgroundDetails.do?contractCode=UT

IMHO, I think you're a bit too big for the road/loop/most sites. Our 30' squeaked in and around but hesitate saying you're good to go.

Our class A is 28' and we did fine. I recall a number of sites that should be okay. You might look at Google maps satellite view. There is also a campground across the highway at the state park. Sites too close together for our taste, but it gives you an option.

There are definitely some sites that will accommodate your rig. I believe there are also a couple of double sites you could get if you're concerned but I think several would work. Sam Stowe campground which is across the freeway also has larger sites with hook ups where you would fit.