I use a ten year-old, slightly modified mountain bike for commuting and touring, and I love it. Last summer, I did a 600 mile solo tour on it carrying front and back panniers, and the bike worked flawlessly. I had to do some creative rigging to mount a front rack on its stock suspension fork (which had only about 45mm of travel), but it held up fine and didn't complain a bit. My only modifications were 38mm wide street tires and bar ends mounted "inboard" to simulate the width of typical road bike bars. (I feel like I'm trying to wrap my arms around a tree trunk when I have my bar ends mounted at the ends of the bars.) I now also have an MTB-style rigid fork which I managed to find pretty cheap. My suggestion to you would be to adjust the bars and seat so you're comfortable for long days in the saddle and enjoy the ride. The bike itself is secondary to your position on it. Enjoy your trip.