Here is a guide on how to get the membership.
1. First sign up at www.prizerebel.com unless you have already signed up. Make sure to use REAL information on prizerebel (But not on the surveys)
2. Then navigate to the surveys page (Get Points>Complete offers)
3. Change the sort to [Credited] [Greatest to Least] (Also described in my first post)
4. Complete between 16-20 surveys (It is best to do surveys worth 0.5 or more points).
*NOTE* Remember to use fake details, except your email (use a junk email which you have access to), some offers require you to activate an account. Also clear your cookies after each offer to get a better chance of being credited. (Check this post for more detail on completing surveys successfully)
5. After you have completed the offers and have 9 or more points, navigate to the prize page and go to page two of the online games prizes.
Both Runescape cards and Ultimate game cards work for Runescape, but I prefer to choose the official Runescape cards.
6. Now you just have to wait a few hours an Voilà, you have the code in your mail!
Just a little side note; you don’t need to complete the whole offer to get credited. What I suggest is to complete half of it, click the prizerebel tab and refresh the page to see if your points have been credited. If not then continue doing the survey.
Good luck, and enjoy!