There is no issue putting the flex right under the tubs...PROVIDED you regulate its temp with a thermostat. If you were to let the flex heat up to max it could melt the tub...but with your thermostat you won't have an issue (this is how most belly heat racks work)


One Herpstat can handle up to 500 watts so it all depends on how many feet of flex you run and what wattage the flex is.