IN response to your inquiry,I have seen this done by a comercial
beekeeper whom I purchased my first Italian bees from.He had built a
fairly large vat(2'x6'x3'deep) which was raised off the ground about 12"
off the ground to provide room for the fire.Parafin wax was brought to a
slight boil and the hive bodies were submerged using a steel weight made
of a length of pipe (2")  with a cross made of angle iron.While this
hive soaked a second hive was submerged in the same manner.The hives
soaked for just over a minute each and by alternating in this way a
large number of hives can be waterproofed in a short period of time.
    Hive boxes treated in this fashion will last in excess of 10 years
without painting or any further maintenance.A couple of hives which i
purchased as used held a paint job pretty well after the excess wax was
scraped from the bottom edges where it had accumulated while cooling.A
word of caution,sink the boxes gently!!! Hot wax splashed on bare skin
burns!!!!!!This works equally well on new, used,or really old hives.The
wax permeates all cracks and joints and fills in slightly rotted
spots.We live in texas along the Gulf coast where the climate is always
very humid.normally woodenware will last 5yrs.if painted regularly.Hope
this helped.
 
                                    Curtis,Pasadena,Texas