Our 2019 Northstar came with 3 2x4s running from front to back. That's all that contacts the rubber mat I have in the bed of the truck. The "Floor Joists" appear to be 3/4" Trex. The 3 main "Beams" which are doubled 3/4" Trex run front to rear above the 2x4s. Then the 'Joists' run between the "Beams" from driver side to passenger side of the camper. There is 2" pink foamboard insulation glued to the floor of the camper between the 'Joists'. If I needed to raise the camper higher, it would be easy to add 3 more 2x4s to the bottom of the existing 2x4s.
