I cook my pork ribs for 3 to 3 1/2 hours at 225-240 temp, basted with diluted Apple juice mixed with a little of the rub I am using. I do that every 30 minutes. I start meat side up for an hour or so and then turn meat down for another hour and finish meat side up for the last hour. I always take the back membrane off. I try to cook with indirect heat as much as possible. Since I don't use sauce or foil I really use a lot of rub on both sides of them for flavor. Maybe that's what keeps in my moisture.
That's about all I can say to help you.