I have a Kohler whirlpool jet tub. I like to add an inline heater to the plumbing so that the water temperature is maintained. Does anyone have experience with installing such an inline heater to an existing whirlpool jet tub? There is a small access door at the end of the tub (opposite end of the faucets) but I have never opened the access door to see how much of the plumbing is accessible.

Thanks