We went to Orlando in September 2000 and only lost two days to rain, and I mean lost.
Was at IOA first thing one day, the heavens opened and it rained all day, didn't even clear up for the evening.
Only other day was when we were driving to the airport for our internal flight to NYC, so didn't really mind too much.
The other 8 days we had in Orlando were fine, I think you've chosen a good time to go.
Have fun, even if it is a long way off.....
Julian