Soon autumn will knock at the door but it does not mean you cannot use a spa.
In fact, many people use their inflatable hot tub in a garage. This is a very good idea. Most of the time Garage spaces are next to houses & they are flat.
All inflatable hot tubs provide a heater that can warm up to 40 degrees Celsius. (104 degrees fahrenheit) so that you will not be cold at all. 40 degrees is more than enough, if you just sit in your hot tub.
Since you use your hot tub in a garage, it will warm up faster. Nevertheless, use the spa cover to warm it even faster.
I have done it several times and i had no moistures in my garage. I also was afraid of problems with power sockets. For the power sockets that were too close to the inflatable hot tub, i decided to protect them with a plastic cover. At night, i used to install the spa cover.
If you look for inflatable hot tubs reviews, i suggest you to visit http://www.revspa.com
don't forget to see how you are going to empty the hot tub prior to filling it up. This is always a critical time when someone empty the hot tub because there are in general more than 500 liters inside the hot tub.