I see from your profile that you haven't been on here since a few days after you posted this. so I hope you do drop in again and get the chance to read this.
Anyway..the track..it's not bad at all..and I think you made the right choice in slowing it down..the mood certainly wouldn't have been the same if you'd just slapped the original over that atmospheric bed.
Speaking of which, if you go back and rework this, you might want to think about reducing the reverb a little on the wind and rain bed..I think you'll find it will help glue the track together a bit more and also help everything sit better in the mix.
Also try playing around with the gain staging a little more, so each element adds to the atmosphere. When it comes to ambient, it's as much about how loud or how soft each sound is, just as much as it's about which sounds you use in the first place. I think you'll find if you mess around with this mix a little more, you'll find you'll be able to tease out that atmosphere even more without changing too much of what you have already..and without having to add anything new to it either.
One last thing, it would be cool if you could expand on what you already have here, making the track a little longer, which you could do by playing around with what you already have, by soloing different elements of the mix up front and slowly reducing the volume on the soloed part, as you introduce the next element, until you end up with the full track..hope that makes some sort of sense, as I'm not too sure if I've explained that too well.
I hope you do decide to go back to this, as I'd love to hear where you take it.