That hot tub setup is almost to a T how a friend of mine had his setup on his under-deck slab. Survived in light rain and no hot sun (here in the south). One word of warning...
We would sit in the tub on the little formed seats and watch baseball games on the TV all the while drinking beers. He would crank it down to about a 99 degree setpoint so as not to steam cook us, but after about 45 minutes to an hour of that, I could hardly move to get out of the tub to take a leak. I swear. My arms and legs felt like they weighed 100 lbs each. But relaxed? Oh...yeah.