I have some experience at sealing up and insulating a garage. That tar fuzzboard stuff cannot be sealed. It's more like a hard air filter than anything else.
My own garage walls never did get well sealed until I had 2" Styrofoam added to the outside and 2" foam dug down 2 feet around the perimeter. I had drywalled and taped the ceiling. That barely slowed down the air leaks. The ceiling got sealed when I pulled out the fiberglass batts and foamed the entire ceiling from above. Then the ceiling got insulated when I blew in about two feet of blow in fiberglass.
In your case, I'd just put in the batts, staple on the plastic and call it good.
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