I was describing my solution to this problem to my friends at lunch last week, and they just couldn't grasp how you could use a beer can koozie as a rudder/elevator/aileron gust lock. So I had to show them...and show off the new paint too
I must be missing something......... It appears to me that you are depending on friction to hold the rudder. If a strong enough gust came along, wouldn't the rudder swing and release the "Koozie", which would then immediately depart smartly downwind?
I guess my response would be: "It will work well, ...... until it doesn't.