I would wrap the entire length of the outside of the baffles. Get yourself some small diameter stainless wire from the women's crafter type store or stainless safety wire from a bearing house for tying the fiberglass on. If you can, find something that mirrors the inside diameter (a round ring or a soup can with both end cut out, whatev) of your pipes for a gauge to assure that you won't destroy your handiwork with the wool and wires when you insert the baffle. I think you will be pleased with the results, if you found your pipes too loud now. BTW, that small diameter opening you mentioned is necessary for low end torque. You can always ream it out larger later on, if you feel the need to.
