I suppose you could use a bead of caulk on the top flange of the jack to seal with the cooler.
How to install evaporative cooler roof jack.
The multi pitchtm roof jack serves only as an air distribution plenum and is not intended to support the cooler s full operating weight load.
Use roof tar or waterproofing membrane to seal all openings.
Install a duct transition piece if needed for a round flexible duct.
Any screws used to mount brackets to the roof should be coated with tar to prevent water entry.
Install a flexible duct from the roof duct to the ceiling register.
Installed swamp cooler on roof.
Install the cooler duct a power wire and a thermostat wire leaving excess wire to allow a thermostat installation inside the home.
You would normally use a leg kit which the cooler would be attached to then the bottom of leg kit would be nailed or screwed to roof under shingles or other roofing material.
Cooler installation kit note.
Set cooler in position on roof jack.
Install supporting leg kit.