I recently added an AC/heatpump for our sunroom. Before winter, I want to close in the crawlspace under the room. I plan to lay 6 mil plastic on the ground as a vapor barrier and use cement siding boards to build the skirting. (There's already insulation under the sunroom floor. Do I need to put some ventilation into the skirting?

I think the rule of thumb is 1 square foot of ventilation for every 150 square foot of floor area of the sunroom.