The Frenzy isn't a whitewater kayak. The molded keel will make negotiating rapids difficult, especially for 300+lb paddlers.
You might consider an IK for these special folks. Or, if you can find one, try and pick up an Ocean Yahoo! SOT. You'll have to find one used.
(I don't know the person posting this)
This boat is a tank and not really suitable for anything above entry level class III, but it's extremely stable and can be fitted with a center-mounted horn that the paddler grips between the knees. IMO, this design feature makes bracing much easier for a neophyte.