Well I usually clean the inside of my windows with invisible glass like every 2 months or so... and I've never had fogging issues after turning on the AC =).

 

i'm about to try this out - i've not had fogging issues with my car as of yet (clean the inside of the windows every other wash, every 2-3 weeks on average depending) - will post up my experience

i <3 rain-x on the outside of my window though, rarely have to use my windwhield wipers

 

I use Invisible glass on the insides every month but that obviously wont help. I will try the rain x again tomorrow and let you guys know how it goes.