Yes I a must admit I'm completely sold on the Arctic way of building the spa !
I would say if a spa needs a winter kit it is not espacially made for cold climates, Arctic has no winter kit and no vents, neither any summer kits.
Arctic insulates as a house, insulation on the cabinet walls not the shell.
It is not true we do put as much insulation as we can in the walls when building a house here, as 4-5 inches will be enough to keep the cold out, so why put in 20 inch? We put the insulation in the walls and double in the roof, we do not put everything in the basement.
Snow will break covers, we had about 3 meters of snow last year, and spas in two of the cabins in this area broke their covers, I agree with Roger, at least buy an upgade. I would prefer to have walked on them to be sure they can take the weight.
As for the floor under the spa it depends on what you put it on, I bought my Arctic with the glassfiber floor unde so I did not need to make a foundation, but put it right on the grass. If you already have som kind of foundation, you probably will not need that.
I have upgraded once and are now thinking of another upgrade, do not know how many people do that, but new stuff is coming all the time.
I still will advice you to open the cabinets to see what you buy, that can't be too much to ask?