I am trying to recall the situation of the underbed storage on my previous NorthStar pop-ups... but I would look very closely before removing any components that make up the storage area under the mattress... that is, it might be part of the cross-structural wood that spans from side-to-side.
It could be possible that the storage area is a result of the "beams" that allow for an upper "flat surface" on which to place a mattress. The flat sheathing below alone may not have enough integrity to support any load should those cross member be deleted.
I am not saying that the proposed solution will not work, but after inspection reveals the possibility then it still might be prudent to call the Factory to get their take on the revision.
Sold the TC, previous owner of 2 NorthStar pop-ups & 2 Northstar Arrows...still have the truck:
2005 Dodge 3500 SRW, Qcab long bed, NV-6500, diesel, 4WD, Helwig, 9000XL,
Nitto 285/70/17 Terra Grapplers, Honda eu3000Is, custom overload spring perch spacers.