WvRider,
I have a 1995 Coachmen Catalina, but looking at the pictures, I'm thinking mine is simply an earlier version of this coach! It is almost identical. Including the delamination problem. Mine is a little further forward than yours but on the exact same side. I too have been concerned with it, but I've never had any problems with leaking or any water damage. In fact I'm glad you brought it up, looks like it's not necessarily a huge concern.
We use ours for weekend recreation and other than the maintanence issues, we've been happy with what we got for our money. Prior to this I had a 35 Fifth wheel toy hauler that we bought brand new. We have the same maintanence issues with this as we did the new trailer, so I think it just goes with the toys. You have to pay to play! However, that seems like a smokin deal on the Mirada. You know your not getting a high end coach, but your also not paying for it either. The first thing I would do is put a Banks Stinger System on it. It will be the best $900 you could spend, make driving much more enjoyable.
Best of luck on your decision.