I have done this with a refrigerator to re liquify honey.  A couple of
things that I learned the hard way are.

1 Get a good thermostat controller.  Kelly's sells one that is a
removable in line device.  That is to say plug into an outlet or source
of 110v and plug the other end onto you lights. Place thermostat bulb
near the bottom so that the hottest area will not get over the
temperature that you have selected.  The mark on Kelly's controller that
indicates the settings is not accurate.  You will need to discover your
own mark.

2 You need a fan to move the air this is very important.  The fan will
keep the bulb cool and circulate the heat.  While heat rises it does not
do so efficiently.

3. You will need to place a barrier over the light I would probably cover
75% of the top of the opening.
I used a 1" pine board.  This board will work as a heat diffuser.  It
will help eliminate hot spots and the air space on the sides of it will
allow air to circulate upward.

I tired this without a fan and with the thermostat at the top of the
refrigerator.  Thinking hot air rises.  I burned $200-$300 worth of
honey.  Very expensive mistake.  Despite the mess of honey coming out of
melted bottles.

Garrett Martin
Willets Lake Apiaries