5th Wheel Exterior Kitchen Vent Replacement - Let's Figure This Out

I need to replace the exterior kitchen vent on my 5th wheel which is old, yellow and cracked.

I've never done it before, so let's figure it out.

Here is the butyl tape I used: Dicor BT-1834-1 1/8" x 3/4" x 30' Butyl Seal Tape