A follow-up to my earlier post on this thread.
The season is nearly over (unless we opt for some cold-weather camping), and the comments I made earlier are still true. We traveled to Verona, VA and Asheville, NC - so we had a chance to REALLY find out how well our Explorer would do towing our TrailManor 2720SL over mountains. Happily, our experiences were "as advertised" by our dealer in Chesapeake, VA.
While we did have to downshift on gear and move to the right-hand (truck) lane with our flashers on, the Explorer moved along at 45 mph and it didn't take long to make it over the top of Mount Afton and other Shenandoah obstacles. Overall, we still got about 18 mpg.
Before next season, I'm going to have the brakes on the Explorer checked, since they are the original brakes at 73,000 miles, and I've relied on the trailer brakes more than I believe I should have to. Of course, "the best surprise is no surprise," which means I should have been driving more defensively in the first place!
Happy Camping!