Just some thoughts for you.
1.Some use a ball under the slide awning.
2. Even with a tight awning you may get water under it on the slide, before pulling the slide in, raise your jacks at one end or the other and this should dump any water under the awning.
3. Also, for some reason you'll find that the long slide may be set lower at the rear then it is at the front. My Tradewinds is.
My Tradewinds was level and we went through some pretty heavy rain, when I brought it in the rain slid off the awning, but the rain under it ran right down the rear and into the MH as the slide top cleared the seal.
Hope this helps you. If you're in a blowing rain storm it will go under the awning.
Joe & Angie
Shih Tzu's Cookie & Rocky
2001 Tradewinds 7390 2011 CRV EX-L Navi w/ RoadMaster FuseMaster