Betty -
To make a VERY simple proof box, start with large-size styrofoam cooler. Throw
away the lid. Mount a light fixture in the bottom. Now, just add a 25 watt
bulb, invert the box, and you have an instant proof box. If it doesn't get hot
enough inside (85F is what you want), switch to a 40w bulb. If it gets too
hot, raise one end of the cooler with a book. For this device we are all
indebted to Ed Wood's excellent book.
After using a proof box like the above quite a lot, I became fustrated because
the temp inside depends on room temp, and so it requires monitoring. So I went
one step further. I bought a very large picnic cooler with a hinged lid. I
mounted a light fixture and a thermostat in the lid. Now I have a box whose
temp will stay near 85F year-round. You need a "Line voltage thermostat",
available in good hardware stores. These directly switch the 110 volt power
from the wall. They are intended for use, for example, in controlling radiant
floors.
Jay