If the gasket is a continuous piece then your going to have to undo the wiring. The gasket won’t fit over the whole unit.
I would download the installation manual for the unit, then follow the installation directions in reverse order. You may be able to skip some steps, but at least you’ll see the order for things for installation.
And yes, you undo the 4 bolts from inside the coach after removing the bezel cover. Be careful when snapping out the two screw caps - they break easily and I couldn’t find replacements without buying whole new bezels (which were prettier anyway - not to mention that if your units don’t have the quick cool vent, a new bezel with the vent is not that much more expensive).