I did mine inside the windshield on my 22 with 1" screws. I don't think you need to thru-bolt them. Make sure you countersink the holes no matter what you do or cracks WILL form. I used a solid brackets(bars) for the rear instead of straps as this takes MUCH of the strain off the hardware as it is like a wheelie bar and then the straps hold down the front. You can do bars front and rear if you wish. It will take a few runs to get the angle right so it does not bow. I highly suggest stainless frames and fittings along with mounts with quick disconnects so removing it takes 2 minutes when putting the cover on, etc.
Nick
1994 22' Classic-454 B1 Red & white
1981 13' Whaler sport(original owner)
South Tampa Bay, FL "May I mamoo dogface to the banana patch?"