Per BPJ's comment regarding lightening ...

Slightly off topic, but I recently purchased a lightening detector - mostly because I hope to be spending more time boating next year. Its the one that looks like an old fashioned pager. It works remarkably well. Pretty slick actually. It can tell me how far away the lightening strikes are, AND whether they are approaching or leaving the area.

http://www.strikealert.com/

Back on topic ...

I tend to think that a good rain fly is huuugely important. If you've never seen them, I'll recommend the Cooke Customer Sewing Tundra Tarp:

http://www.shop.cookecustomsewing.com/category.sc?categoryId=12

Another thing to think about is how your tent door will function in rain. Some - like some dome tents - are terrible in rain.