Which Tempest?
There are two sizes in poly: 165 and 170. You didn’t specify what you mean by “cavernous” but at 5’2" and 110 lbs I found that adding 1/2" minicell foam padding to the 165’s seat made it fit very well. Edging is easy to control yet I have enough room to swivel all around, get in and out any way I choose (both legs at one time, for example), yet I have just enough clearance to do a full layback roll. Comfortable enough to paddle for hours without stopping.