After spending a cold night in Alabama, we bought a wireless indoor/outdoor thermometer. I installed the “outdoor” unit inside of our “tackle box” mounted on the rear of the van. Although it’s inside of a wooden box, at least it’s outside of the van. We attached the interior monitor with Velcro so that we could move it between the “downstairs” and the “penthouse” top bed area. The cost was $10 for the thermometer unit and $2 for the Velcro at Wal-Mart.