Bolts, nuts vs. cotter pin set up on roof vent covers?

I recently cleaned my vent covers on my rig and noticed that my Fantastic Fan cover had a fancy cotter pin hinge set up. Quite convenient, easy to remove. But, the other vents above the bedroom and bath had bolts with a washer and split washer. Those are a PITA. One nut would not screw off the bolt. (There's always one, right?) I had to hacksaw the bolt off to get the cover off. :h
Has anyone replaced all the bolts with a type of bolt with a hole and then inserted a cotter pin set up? It has to work so the cover is on securely but easy to remove when needed. Any suggestions would be helpful. Thank you. :)