Sounds like a pretty good, long trip. I was in and around Rapid City, SD around the time you were(July1-5). I have a trailer approximately the same size and was at the Rapid City, KOA. Spend five days in that area, checking things out, sightseeing, etc. I was a good thing the trailer has a/c, it was hot and muggy.
I went west from there into MN, then back up to Canada. It wasn't as long of a trip as I would have liked, but it was good. It pulled pretty steady, and was powerfull enough to pass GMs, and other midsize SUV's stuggling to pull theirs. It's just too bad the gas tank doesn't hold very much fuel. The gas in the U.S. is cheap compared to was it is up here in Canada. Anyways, I liked the 4.00 a gallon price. Up here, with the conversion, gas is like 5.29 a gallon(around 1.40 a litre up here).
Have a good day everyone. Peace.