I also agonized over the AC question before placing my 4x4 van order since the Starcool option is no longer available. (My understanding is that they stopped manufacturing it.)
Here's what I learned. It's EITHER the Pro Air AC option that only works while the engine is running OR the Danhard AC that only works when you have a shore line.
Since I intend to travel with the wife and a grandkid or two, having AC in the back while driving was a higher priority. I also will not likely be having a shore line available most of the time. I'll just avoid really hot & humid destinations during the summer. (I still think that leaves me a lot of places to visit.)
My van has just begun it's interior build so I asked SMB to respond to some of the comments in this thread. Here's their reply: "ProAir does have a 12V/110V system that is designed primarily for ambulances. We do not install it on the vans because it is so big and it requires a ton of power. Most likely k9sprinter had that system installed by one of our other facilities because we have not done one here. I would assume it was done on a Sprinter. The one we install here is a 12V one that will only work off the engine." I would add, or you can select the Danhard/shore line option.
Believe me I wish there was a better option. I hope this helps.