I wouldn't hesitate to go on a long trip with such a vehicle, assuming it checks out mechanically. I would, at least for the first long trip, try to avoid having to adhere to a tight schedule. If you need to be 1500 miles away in three or four days, say for a wedding or something, then a breakdown could easily cause great consternation.
I would also be prepared (with available finances etc.) for the possibility of something breaking down. Most breakdowns would probably be something in the house part, and many of those often can be worked around with a little additional hassle or annoyance. You can keep food in a cooler rather than the fridge, you can heat water on the stove top rather than with the water heater, etc.
If you go in with the expectation that everything will work perfectly, you'll stand a reasonable chance of being disappointed (and that's unfortunately also true often for newer RVs). If you go in with the expectation of having an adventure into the unknown and a sense of humor about what comes up, you're pretty likely to succeed and have a great time.
