OK guys, perfect timing. I just got back from BusN USA yesterday and just started in on my project to add the third AC and relocate the front AC. Also, I am the guy that started the other thread on straddling the center rib.
The units I am working with are the Carrier Air-V units mentioned previously. The cold air inlet does have a short flexible connection to the distribution plate. This opening is offset so that it runs from 6.5 inches to 12.5 inches - offset to the driver's side. The return opening is 2.75 inches by 14 inches running across the opening (from side to side).
So, it is possible to offset the unit about 1.5 inches (perhaps less) to the drivers side and not have the center rib disturb the cold air supply. The center rib would cover a bit of the return air opening. If your rib was 1 inch wide (mine is less on the top side close to the opening) you would cut off less than 8% of the opening. Actually it would be less than that, as there would be some clearance between the rib and the bottom of the upper unit.
Bottom line, with proper planning, for the Carrier Air-V, you can straddle the center rib with some minor offset.
Having said all of that, I am going to make a tubing frame, cut the center rib and weld in the frame. The front cross tube will be welded to a cross member to give extra structure. I did not want to offset with the Eagle, since it has a fairly rounded roof and the Carrier units are quite tall (and a bit ugly
). Any offset would probably be not be noticeable to most folks, but it would drive this engineer crazy (wife says crazier