We've had our '04 23B for four seasons now and there's a few things we've experienced over time.
1) The AC bolts were definitely loose. They tightened them when I had a local dealer do a complete inspection, but it had caused a little sag in the roof that's just there now.
2) Anytime the unit is not in use, it's parked on an angle which reduces any pooling in that area.
3) However, I learned that if we are using it and we get heavy rains, I need to tip it and drain off the roof before starting the AC. Last year I couldn't figure out why it was leaking water anytime I turned the unit on until I tipped it and all the water came off. Problem solved.
4) Check the seals on your storage compartments. I learned the hard way that a leak will let water enter in. Ours failed during the off season so when I went to get it this spring, I found that the opposite end of the camper had a soft spot right before getting into the bunk. What happend is the water entered through the failed seal, got all the way under the linoleum, and because we tip the unit, traveled all the way down to the other end and caused the wood to soften. We haven't torn up the floor and replaced anything yet, but will keeping an eye on it for sure.
All in all, we are really big fans of the unit and have zero regrets about having purchased it. Nothing that has ever happened has made me think that shouldn't have happened. Just stuff that happens.