I have the underdash unit you're talking about. It has been awesome! Very easy install.
CAA has you drill two holes near one another to pass the hoses through the firewall. If you drill them too close to one another, it's easy for the thin firewall metal to get twisted and pulled out. This is mostly because there's already a kind-of cutout in the area (cylindrical pill-shaped) where factory AC hoses ran. CAA has you use two holes and two grommets; however, you can also just punch out the factory cut-out and use the factory grommet if you get one. I wish I had done that from the get-go as I took the two-hole approach and the firewall tore while I was messing with the hoses. System is now charged so I don't want to drain the freon to pull the hoses out and really punch out the firewall correctly, so instead I had to put a lot of sealant around the hoses to seal up the gap in the firewall. Kind of annoying
As far as other tips go, take the time to make sure that your underdash register is properly centered (espeically if you have a center console) or it will be very noticeable later. Also be careful not to torque down the bolts holding the dash mount bracket to the adjusting sliders on the unit too much, because the slider can actually get pulled partway out of the unit somehow... still not sure how that happened but it happened on mine.
Otherwise, should be a very painless installation! I think I remember doing mine in a day or so. Ultimately, it's just drilling a few holes and then attaching parts to other parts - not a whole lot of critical thinking required
And FWIW, I've never had defrost issues with my car even without the integrated defrost feature that the other CAA systems have. But then again, I always have my window down (or at least the quarter vent open) regardless of the temperature or weather conditions, so that's probably why.
1966 Modified Fastback - Driven semi-daily!
and rebuilt even better
289 v8, 4-speed, 3.25 9" rear, goodies and stuff.
See my travel blog here for my adventures: http://calamityjaneroadtrip.blogspot.com/
2014: 10,051 mile, 2-month-long road trip around America
2015: 3,000 mile trip to Knotts in CA, CO to East Coast, an engine rebuild
2016: East Coast to TX, Hot August Nights, more trips to the East Coast
2017: Several long trips in the works! Stay tuned