I find that the Meguiars foam hand applicators are ideal for Opti-Seal application. I only apply OS to the pad-and make sure you not only initially spritz the middle of the pad, but out by the edges, otherwise the pad might be grabby the first panel or two.
Helpful hint: If it takes longer than 30 second for Opti-Seal to dry and clear out, you are using too much. Even in 40 degree weather, OS was drying faster than 30 seconds for me.