its all about maximizing the heat when doing solar method. The flake wax i bought has a meting point north of 170 degrees, so how does one get to 170+ on a 90 degree day? Black, control the heat both top and bottom of container, and full on sun. your dry dirt has to hit that same temp for the wax to melt and to be soaked up by the hot dirt.
I had good luck using a concrete mixing tub and a THIN layer of presifted dirt in that with right amount of wax flakes stirred in. Then i put it under the black tonneau cover of my pickup bed and let it sit their all day in parking lot when I was at work on 100 degree days. Worked well.
Here is my solar set up and it gets full on sun or goes under the tonneau cover of the truck.
If using hot beds like plexiglass or clear thin plastic cover then yes make sure the bottom also is on a surface that heats like a black sheet of plastic on driveway. Its all about maximizing heat in solar method.
Interior of an old car sealed up gets really hot on a 100 degree day but the dash in full sun would be hottest place. Just think like that when using solar method. Nebraskacatman uses solar method too and I bet he has good hotbed setup. Check with him.
I've been making small batches in an old crockpot set on high. It works but only does a gallon at a time...which actually isn't much less than when I spread it thin in the mixing tub and stick under my black tonneau cover so I still crank out about same amount just able to do it whenever I want to using the old crockpot.
Jim
Here is dry sifted dirt with flake wax mixed in...
Here is after wax has been melted and thoroughly stirred in, that wet dirt look right?
And when its done I dump it out into this old concrete mixing tub and keep stirring it. I use that tan spreader. Do this while it cools to keep it from clumping until completely cool, then put it in containers for use on the line.
The F&T guys had some great video clips out on solar and so tonneau cover methods. MnTrapline has stuff on their website too. Lots of good YouTube videos out there too.