Hard to believe, I'd be interested to see a picture of that!
1/2" foam board or thicker?
How was it fit in their steel structure?
Would be interested if it came from factory like that or local MN dealer fit it for your climate.
My Maax has this for insulation:
http://www.bondedlogic.com/oem-solutions/spa-insulation3" single foil side
I took an IR thermometer to my tub's exterior for weeks, and I can say with some certainty that the heat loss is from the top lip of the shell
where it is covered by the flap of vinyl coming off the cover.
When I purchased, I considered adding foam board (if wrapped) but haven't felt it was necessary.