wbullivant, This is an interesting and important alternative to roof air. Posting the pics on this site could insure they are always available. I can see how this could be modified for a side wall also. Do you have any performance experience to share? My intuition wonders if the single 4" in/out vents are adequate. Looks like doubling that to both sides would only add a few extra inches. Thanks for sharing.
Two 4" ports work better than one 4" port. I have two on discharge side which can be easily closed off, so I tested with one versus two and it does affect air flow some. It also affects current draw a little because head pressure goes up, making A/C work harder. In cooler weather it's not as important but in very warm weather it can be more critical if A/C shuts off due to high pressure.
I do not use screens in large part because it limits air flow. Since my A/C compartment is not open to rest of van or storage compartments, I did not see the need in that it's no different than installing same A/C in your window at home. I do close the vent ports when in transit, or van is not in camping use or A/C is not needed. In over 10 years I have not had any pests or animals get into system that I'm aware of. When I occassionally pull A/C out for inspections, area has always been clean.
These kinds of window units are being used on many trailers and even motorhomes, but with the difference that condenser discharge (back of unit) is free to flow into open space. If you read most manufacturers' installation instructions, they state not to place objects within a few feet from back of A/C. We have to break that rule, but should keep back side as open as possible in my opinion.
I would highly recommend not placing the back wall of compartment so close to A/C discharge as shown on his pictures. I know storage is important, but I'd personally sacrifice a little space and move it back at least to other side of 4" port (or ports if you use 2 ports). You want as direct a path as possible.
Lastly, I designed mine to add a fan if needed to supplement air flow, but it turned out it wasn't needed. I prefer to keep it simple because if not sized large enough it can actually restrict air flow. On my A/C the condenser fan is fairly large (in range of 9" in diameter, more or less) so it moves a lot of air. Picture of my two discharge ports below.
Your results may differ since details can make a big difference.
P.S. -- For what it's worth, I did see a Ford van with an 8,000 BTU/hr window unit installed inside which worked OK from 8 batteries and an inverter, but A/C venting was a absolute mess; which was one reason I passed on buying that particular van. That an cost was too high.
