I use a couple of these low profile oil filled heaters and they would work great for something like that.
With no visible flame or red hot cores makes them safe as can be sitting there unattended...
These 14-inch tall units were got for my POPUP trailer and are just the perfect height to sit one of those 10-inch O2COOL Battery/12V/120V portable fans behind it if you need to move some heated air around...
These THERMO CUBES are neat to have as well... I plug in a couple of the 100WATT incandescent bulbs in them behind the cabinet doors. These come on when the temp drops to 35degrees and stays on until it gets up to 45 degrees...
This is my plan of attack for sitting parked here over the winter months...
Roy Ken
