New Full Time Camper in need of insulation advise.

An additional question I have is; after skirting, would gluing/stapling more foam board or some other type of insulation to the under belly of the camper help? I read that 25% of heat if lost via the floors. I might want to eventually use spray insulation to redo the factory insulation before next winter. Also as far as electric heaters go, what type of electric heater works best within a camper?