William, I am a Techflex dealer and would be more than happy to send you free samples so you can see what size best fits your project. You may find that a few different sizes will "fit" (because of how much it expands), but each one will give a different look or feel. Because it's hard to know what the end result will look like, I offer samples of different types, sizes, and colors of Techflex to anyone in the lower 48 US for free, anywhere else if you provide postage.
If this violates forum rules, please let me know and accept my apology. I'm just a fan of the product and like helping fellow DIYers. Cheers