As Steve says, 3/4". My tank is standard thickness though and hasn't given me any problems so far, but it isn't summer yet.
Another thing is the existence of insulated tanks from aquatico, but they cost more.
What I've done with my tank, although it's a hack job, is glue styrofoam sheet on all but the front. Also, having the tank on top of stryo sheet goes far. Thermodynamics and stuff y'know.
As far as Puget Sound goes, use GOOGLE image search, terms like Puget Sound scuba etc. and you should get some good results. The marine biodiversity here in the sound is extraordinary, I may be incorrect but I've read somewhere or heard that there are more species per square foot here than anywhere else. Another thing is that with the critters from here you can pack more variety into the tank and not have the compatability problems as with tropical reefs. I really am starting to prefer my coldwater system over the tropical for that reason, plus I collect for myself, which is a blast. Additionally, the maintenance with my system is much, much less than the tropical. Almost zero evaporation, no algae issues, I just go and get about 20 gallons of water per week from the bay and that's it.