We don't quite match your usage, but we put on a lot of miles travelling cross-country twice a year. When we are in the west, where distances are big, we do a lot of camping as well. We have had no mileage-related or heavy-usage-related problems in two years.
Remember to
- Monitor the tire pressure religiously, and keep it at 50 psi.
- Grease the wheel bearings with the proper grease every few thousand miles - it's easy.
- Grease the hitch ball every couple uses.
- Put a bit of lube on the springbar stubs every time you hook up.
- When you are ready for the road, weigh your TM with the springbars in the travel posiition. Don't overload! Even with "reasonable" loading, you will be close to 3500 pounds, which is the axle limit. (The tires will take a few pounds more.)
The problems we have had have been minor, and would have occurred no matter how many (or how few) miles we racked up. There was ony one exception to that statement (bolts pulled out of the hold-down latches on a real rough road), and I believe that weakness has been corrected on the new models.
Enjoy
Bill