Hi and welcome aboard.
Just to the west of you, next state, and it's cold here too. My toy hauler is in winter storage until spring. Too darn cold to use in the winter months.
Can't help you on the underside insulation however.
Edit to add:
Suggest you visit your local Camper Center or a manufacturing housing dealer as either will know about undercarriage insulation.
2012 Fun Finder XT 276 Toy Hauler & Harley Davidson Ultra Classic with Condor wheel chock
2014 Dodge Ram 2500 AT 4X4 Crew Cab 6.4 L Hemi, 373 gears, tow package, Rambox option, Revolver X2 tonneau cover, Equal-I-zer anti-sway hitch.