Somethin you may consider  is foam rubber  on the inside of the roof. I
think I used monmouth rubber.com.They can send a sample sheet of rubber
samples on request. Got a big sheet of 1/2 inch by 6 feet by 9 feet of
neoprene rubber and cut and glued it ot the roof. They have about 15
different kinds of rubber.It makes it a bit snugger.Gotta cut out for the
skylight ect.