heat in the lower storage bay

Depends on the size of compartment, insulation, and how cold things get. I would argue that a 60 watt old fashioned bulb is considered "inefficient" because most of the energy is wasted as heat vs light - in a tight compartment that heat is constant and builds up .... might compete with the heat generated by RV furnace which tend to vary by distance,furnace BTU, and thermostat setting. Be interesting to see a test.

Long story short - not much downside in putting a light bulb in the storage area - if it's enclosed and has ducted heat - consider it insurance. If it's not ducted then it's likely your only alternative.