Hi,
I advocate using heat strips. In your situation I would return them.
My next favorite is oil fill heaters that are 1/2 size and can be tucked into unused corners that need a bit of extra heat.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.