In my 13 foot Scamp
I plug the thermostat in at the end of the kitchen counter. I place the heater on the floor, right in front of the kitchen cabinet, near to the bump up to the "dance floor" under the bed. Placing the heater in this corner, slightly away from the cabinets works well to keep it pretty much out of the way, plus the toe kick area assures that there is plenty of air flow behind the heater. This location keeps the cord from running across a walk-way. When the heater is not in use, I just set it up under the bed out of the way.
I rarely have to run the heater above the low power setting to keep the trailer pretty toasty, even in single digit temps. I add reflectix insulation to the windows
and ceiling vents - makes a tremendous improvement in comfort. Plus add either throw rugs or, better yet, the interlocking, cut to fit, foam floor tiles that are available at any home improvement store. These are easily removed again when the weather warms up.