This was part of our route 2 years ago coming from PA and heading out to Yellowstone and other points west. We took 29 out of Omaha up to 90 in SD. Ended up staying at a Walmart in Mitchell SD, which was great. I bet there were 50 other RV's and campers there... really felt at home and safe. There was a Cabela's connected to the same parking lot.
From there we headed out the next morning across 90 and took 240 down into the badlands and back up to Wall where we got back on 90 and headed to Custer.
29 and 90 are an easy drive, flat and smooth... a monkey could drive an RV across those stretches of land... 240 is by no stretch of the imagination a "difficult" drive, but I suppose some people might not appreciate the switchbacks and hilly terrain once you get into the bowels of the badlands.
240 is also called the badlands loop scenic byway. It must be about 30 miles total, and takes you past some tremendously scenic stuff... it is a very hilly route, and there are some points along the path that kind of make you pucker up a bit... but I wouldn't hesitate to do it again. Most of the people driving that route are sight seeing, so you can take your time navigating the curves and hills, and if i recall, there are plenty of places to pull over and let the traffic go by if you're feeling self conscious about your speed.
We did this route in a 35' motorhome. I wouldn't be afraid to add a towed vehicle behind me and do it again.