Usually not heaters, but it uses the ducted heat from the floor to keep the underbelly above freezing. Unless you paid the dealer to install something, Jayco as far as I know is not installing heater pads under the tanks in 5'ers. MH models may be different.
My last unit had the 4 season glacier package and that was considered a heated enclosed underbelly. I do not know if my new unit will be different, but I do not recall reading anything about heater pads in the specs.
2014 375 BHFS Eagle Premier
2014 Ram 3500 Longhorn DRW CC
6.7 CTD, Aisin, 4.10's