[hbens]

Nice job. I especially like the retrofit and use of existing ductwork. Air flow is the key base on my observations of other conversions.

Before you cut larger holes in the bay doors to increase air flow, you might play around with a fan or two forcing air through the existing opening. If that works, it would be a straight forward task to add a couple of pancake syle radiator fans to the inside of the door. Then trigger them from the AC controls via relay.

Richard, thanks for the idea; I'll have to determine if there is enough room between the condenser and the inside of the basement door.

I installed two of these radiator electric fans. One pulling in from the curb side and the other pushing out from the street side. I used remote controls I found on AMZN to control these fans from the salon. 
I also installed inline fans in the 3" or 4" ducts to the bedroom and bathroom also controlled by remotes.
The fans gave me a couple of degrees cooling benefit.
When our coach is in direct florida sun I measured the coach skin temperature and it was 134*!!!!! It doesn't matter what color of paint I shot at the temp is way up there.
No wonder our AC units work so hard down here in FL.