Hi there, I have a question regarding vent cap install on exterior wood siding as seen in the picture. The 6" vent cap is for a new bathroom exhaust fan and made of galvinized steel. The problem is there is no holes round edge of the cap so I can't use screws to secure it onto the wall siding. Is caulking along enough? if is what type of caulk or adhesive would be good for this. Should I nail through the metal flashing to secure it? Thanks.