Thank you for the plug.
If I may ask; why have you decided not to use ImperialGaskets? If it comes down to spending more money on this kit than you wish to spend, I do have some "seconds" that I sell at a cheaper price.
I've tried gluing together rubber tubing, ribbing with cord and latex, using a large rubber inner-tube, with little luck.
Other than rendering rubber, sewing ribs in foam is the closest match that I can find.
Whatever you decide, good luck and please share your results here.