Grain dryer is portable because an old trailer axle has been mounted underneath the lower frame. A two ring dryer like this can hold over two tons of grain, so block the plywood box or plenum up on all four corners to support the weight of the grain. Make sure the dryer is positioned where it can be easily emptied. Do not try to move the dryer when it is full, because the tires and axle will not support the weight.
To develop proper static pressure the floor must be entirely covered with grain. Bare spots on the floor will channel all the air so the grain will not be evenly aerated. Very small amounts of grain can be dried as well as full loads. If you wish to use some kind of low temperature heat source channel the heat to the front of the fan. We have had good success using a two foot diameter cardboard to conduct heat from a wall heater to the fan. Test grain moisture often and dry to the recommended moisture for long term storage of beans, grain and oil seeds.