Cassette AC units for Mobile Homes

The unit has 2 12" ports. I have been looking for some kind of prefab mobile home skirting trim kit for either the Insulated duct tubing or 2 12" galvanized duct tubes. Even something as simple as this basic drawing.

I have a chance to do a few of these this summer on the side and the units themselves are all the same size.

I used to help run large duct work in factories and the bigger stuff is so much easier to deal with.