I have chronic lower back pain. Sleeping on the ground seems to hurt it; riding my bike doesn't. In fact, I think my riding position on my road bikes with drop bars helps stretch out my back and helps the situation.

A few millimeters here and there can make a big difference in comfort, especially if you're riding for several hours a day, day after day. I'd suggest playing with your setup on the 520, since it's an excellent tourer. You can raise or lower the saddle to get better leverage with your legs and less butt pain. You can slide your saddle forward or backward to change your reach to the bars. You can rotate your handlebars up or down. It might help your back, or not, but it also can make your hands and arms more comfortable on long rides. All of these tweaks are free.

A tweak that may help your hands (and back?) and will only involve new bar wrap is to slide your brakes backwards or forwards. Having the hoods in a good spot can help with hand comfort.

A tweak that costs a little more is to change your stem. You can get more or less stretch, and raise or lower your bars. It only took me two stems to get the one I liked. My first one stretched me out too far and was too low. My second one raised the bars until they're almost level with my saddle, and brought the bars back to a comfortable reach. My bike now "fits me like a glove."

Some people love flat bars and tour on mountain bikes or hybrids. If it works for them, who am I to criticize? I just know I wouldn't want to tour on my mountain bike unless it was off road.

Some people swear by recumbents. I wouldn't know. Maybe someday I'll try a tour with one.

I think you can find a comfortable ride that won't hurt your back. Sleeping on the ground, however, may be an issue. The best lightweight pad I've used is the Big Agnes Insulated Air Core air mattress. I have very little pain in the morning and it's comfortable all night. It only takes me two minutes to blow it up and a relaxed pace and that doesn't bother me at all. I've also heard wonderful things about the "new" NeoAir by Thermarest, but it's too expensive for me to buy just to try. If my Big Agnes ever gives out maybe I'll give one a try.

Have a great tour!