I hear you about the vents. We were concerned about that even before the HVAC was turned on so we tried to incorporate as much extra stability into the plane as we could.
See here at 1'27" into the flight: https://www.youtube.com/watch?v=rt8HQGQ ... e=youtu.be
The plane flies directly under a vent (2nd time in the flight) and gets blown down about 5 feet, but stays stable. I think the flight would have been over 1'50" without the HVAC.
We compensated for the small stabilizer with a very long tail moment (5x wing chord, 40cm), which I think is longer than the kits that are out this year. In order to avoid nose weight, we endure two compromises: The tail boom, tail feathers, and rudder trim mechanism are minimal and they need TLC in use and in storage. Also, the nose moment is very long. That does have the advantage of supporting a very long motor without risking it falling off mid-flight. The downsides are that the motor stick is whopping 18" long and we need to judiciously taper it to avoid going over the 8 gram minimum, plus the mid-point of the motor is not on the CG so we need to re-balance the plane with each change in motor weight.
I don't think it would be difficult to modify a kit accordingly. HVAC is an unavoidable inconvenience in many parts of the country, and I suspect the kits were designed in the late Summer when HVAC wasn't a problem.