There is a kit sold on Amazon or E-Bay That mounts on the tube at the foot well. It is like an air scoop about 10 inches long on the outside which is mounted over a 3 inch hole I believe and also you can open and close the vent from the inside. I think Summer Breeze said it was sold as a Slingshot vent and has it installed on his SS. He says that it works. I will see if he still has the info where he ordered from when he gets back home.
I purchased two items on Amazon, have not installed them yet, but they were from a suggestion by others.... This piece goes on the outside facing forward, and the vent goes on the inside
MagiDeal Pack of 2 Car RV ATV Camper Interior Round Ceiling A/C Vent Air Outlet Rotating Open Close
Etopars™ Black 2" 52mm Universal One Hole Dash Dashboard Car Gauge Pod Mount Holder ABS