I don't know that there is a big advantage to the two bolt system as far as strength, but there are a few other bowyers that use the two bolt system. One advantage is being able to drill both holes from the front of the limb. You can drill one hole and then line up the limbs on a flat surface and drill the second hole. By using a second bolt you don't have to put and overlay on the limb to cover the hole that extends all the way thru the limb.
A gasket of some type is helpful to eliminate the possible squeek between to two dissimilar surfaces. There is numerous materials you can use as a gasket and rubber is not a bad choice. I've tried rubber, fiber gasket material and often use the clear shelf liner paper because it is self adhesive and once on it is really hard to see and takes up little space.