Allen,
 I was waxing yesterday and put in a thermometer.  It read about 280°.  That
seems hot enough for me.
  I have not noticed any brittleness of the wood, only that it doesn’t crack
or warp or rot.  The paraffin is sucked into the pores on cooling, so only
surface weathering is noted.  As for the time of 15 minutes, that’s what
they do in HI at Kona Queen.  A longer dip sterilizes the wood completely,
uses less wax, and leaves less wax on the surface, which can cause slippage.
High moisture wood may shrink or warp during the process.
 Excluders do sink to the bottom and occasionally get a tinge of char where
they rest in the propolis that also sinks.  Filtering the paraffin through
cloth over another barrel next to the hot one is a good idea from time to
time.  Another possibility is a metal rack to prevent excluders from
reaching the bottom.
 I’m not sure why the Australians don’t like the waxing, (it's used
extensively in NZ) but for termite areas, a copper napthenate soak and
drying before waxing is recommended.
Regards,
 Charles Andros
 Linden Apiaries since 1973
 Former NH/VT Apiary Inspector '78-’89
 1 McLean Road
 Walpole, NH
 03608-0165 USA/EUA