You can contact the support email firstname.lastname@example.org to go over your sizing issue and we will make you a custom tapered sheath if required. We will not charge you for this service as you have made several attempts to find the right size already.
Please mention your username and ask for assistance from Bruce.
btw. as you mentioned, when using the spandex sleeve to thread the sheath of the innerwear on, it can be a bit tricky to pull off after it has served its purpose. In this case, you need to experiment with the optimum placement of spandex sleeve on the shaft. It should be no more than halfway down and even less for it to slide off more easily. Of course if you do not place it far enough down it will come off too easily in which case you can experiment more to find the optimum placement.