Anybody who drives these old crew cabs knows the way the roof acts as a drum. On various internet sites there are frequently debates as to how to deal with this if you are building a diesel truck and you want to be able to carry on normal conversations or listen to the radio. Many people are against filling the space between the ceiling and roof with foam is a mistake just asking for rust issues. I disagree. Year ago I filled the roof of this truck with foam. It has been sitting outside ever since. Before I filled it, I had too repair rust all the way across the top of the windshield. To this day, the rust has not returned and the roof just makes a dull thud sound when you knock on it.
Long story short, I am filling the void in the roof of this new cab. I attached a longer hose to the cans of Great Stuff to reach deeper into the recesses.I happen to have some hose that fits over the Great Stuff straw perfectly.
Being the brute that I am, I went ahead and bored some holes in the ceiling that are the same size as the rubber plugs that cover the body mount bolt holes in the floor. I plan to make headliner inserts someday to cover them, but I really won't mind if the rubber plugs are visible indefinitely.
When it was all done, between three new holes, the sunvisor holes, and the rear dome light hole, the roof is now full and muted.
Just a little trimming...