Omaha to Capulin Volcano NM

Can’t really help with the route. But I don’t think you want to tow your 5er to the volcano. Narrow steep road to the top with a small parking lot that would be hard to turn a 5er even though it has a few RV spaces probably better suited to a B or smaller C mh. The visitor center at the entrance has a somewhat tight parking lot with some RV spaces where they may let you temporarily drop the 5er and drive to the top. Call to be sure and check satellite view. Better yet is to stay at the small RV park in the town of Capulin.

There are a number of routes there but if it were me this is my choice: I80 west to I76 into Colorado: at Brush CO pick up Colo. 71 south; stay on CO71 to US350 which is south of Rocky Ford; travel south to Trinidad CO and pickup I25 south to Raton NM: pickup US64/87 east to Capulin NM. This route avoids all of the busy metro areas along I25.
I agree with BB, drop the 5th wheel at the campground in Capulin and drive solo to the monument. I did tow mine to the headquarters and it was not an easy run, but there is parking at the headquarters. Call ahead to be sure the road to the top is open. It has had repairs at times due to rock slides.

If you don't like I80 you could look for a route to I70 in Kansas and then to Limon CO, then south.

Enjoy your trip.

Thanks so much for your help and advice. We are planning to leave our fifth wheel at the campground and tour the volcano area in the truck. So many great and unique things to see and experience in this wonderful country!