I've owned a pair of Seamasters, one kit bird & one ARF. Neither had the stab re-infoirced & neither stab failed. That doesn't mean that it can't happen -- if you are nervous about it, beef it up with external struts.

The old kit Seamasters could be very heavy if not built carefully (10 lbs). If that is the case it will need a diet to perform well on an old .52 four-stroke. A modern .52 4S will work well.