Didn't use doweling but I have used inexpensive backer rod sold by Home Depot. It's used to create a backstop when caulking & you need to fill a gap to hold the caulk in place. Don't remember what diameter I bought but I'd insert about 12" down the shaft & push it down the shaft with whatever's handy to snug it up a bit. No need to jam it down the shaft & compress the hell out of it.
There was much discussion about open-cell and closed-cell but I don't remember those details. One was supposed to cause shafts to rust by trapping moisture but I played a set of M05's with Rifle 5.0 shafts for years and never had a shaft fail.
I found that there was less vibrations resulting from toe/thin strikes & my wrists and elbows were extremely appreciative.
