I have an idea that may help to combat the temperature swings as the Smokin Tex (can we start a new acronym here? I'll just call it the STX) gets going. I have gotten into the habit of using the drip pan that comes with the STX as a drip/liquid pan inside the smoker. I put it on the bottom rack, under the meat to catch the drip, and i often use that drip to make bbq sauces especially when making brisket. When i cook pork I always put liquid in the pan before starting the smoke, usually a mix of AJ and water, probably a cup or so of AJ and then a few cups of water. This really helps the tenderness out and it will combat the dry texture you're getting.
Additionally, this technique can help fight the temperature spikes because the liquid will absorb alot of the extra heat and just make steam when the STX gets too hot (think back to high school chemistry - remember all the heat that water absorbs as it stalls at 212 degrees before evaporating?) and it will also keep the internal temp warmer when the STX drops below your set temp by acting as an extra reservoir of heat. I really think that this technique has helped me get consistency out of the STX. It also keeps the STX cleaner because your drippings don't get all over the inside of the smoker.
I still wrap the meat in foil about halfway through and put a little AJ inside the foil before wrapping up tight. Make sure the foil has a good seal because you want that steam to stay inside the foil.
Additionally, you want to leave the smoker door open as little as possible. If it gets too much air the wood will flame up and make unwanted soot leading to bitterness.
You might also try a light coating of yellow mustard or olive oil on your ribs before adding your rib rub. This helps create a nice bark which will also contribute to moisture retention.
So your baby back process might go a little like this:
1. place a few ounces of wood chips or chunks in box, turn smoker dial to 220, place pan on bottom rack with apple juice and water and close door
2. remove membrane from bony side of ribs
3. apply light mustard or olive oil coating
4. sprinkle rib rub on ribs and pat into meat
5. place ribs on smoker rack 6 inches or so above the liquid pan
6. insert meat thermometer if desired, and close door; set timer at 2 hours (don't add anymore wood - the initial amount is enough)
7. at 2 hour mark, wrap ribs tightly with foil, pour in a few tbsp of apple juice before sealing foil wrap, and place foil wrapped rib rack back in smoker, set timer for 2 hours
8. at conclusion of time, remove foil, place ribs back on smoker
9. apply thin brushing of sauce if desired for wet, sticky ribs, otherwise simply take meat out of foil and put back in smoker for another hour or until desired temp is reached. No additional wood needed for the final hour or so.
10. At the end of the last hour, remove ribs from smoker and make a little foil tent over the top of the ribs so that the sides are open. Let sit 20 minutes or so, cut, and eat...
with this technique i have been getting good results. I use Jeff Phillips' rub on my baby back ribs because I like the subtle heat mixed with the sweet smoky flavor it makes. I also do not put sauce on the ribs after foiling (or even while eating! haha).
I really hope this will help you. Please let me know what kind of results you get and please keep us apprised of your questions and results!