You should be fine. 10 mil is a decent thickness and having grommets every 18" is a better way to go.
Last year we were camping at 7:15 & C (C frontage) on the side away from the man. I setup my monkey hut broadsides to the wind coming from the SW, I didn't want to create a wind tunnel having the opening face into the wind. I brought the tarp down on that side all the way to the ground and cinched it down with a rope running the length of the hut, weaving it between the grommets, as you will see in the pic below. I ran ropes the length of the hut on both sides and attached them to rebar every 5 feet (see pic).
Plus running a rope over the top of the hut between each rib, also anchored to rebar (see pic). Creating as much structural tension as possible. Things will move a bit in a wind storm which is fine, you want some give but not so much give that the pvc comes free of the joints at the top.
The guy who modified the Monkey Hut and is calling his the Galaxy Hut has some good ideas that I incorporated into my monkey hut.
http://galaxybeing.com/galaxyhut/
Keep in mind the wind can and will reverse on you so don't build up one side only.