Nitro is a fiberglass bass boat division of Tracker if I recall. Maybe Tracker uses/used it in their aluminum boats. My neighbor just bought a 2017, Tracker 2072 Grizzly and it is all aluminum. You can probably find an access port adjacent to the transom where you can reach in and feel/have a look.
Balsa was a deck (floor) filler on Kingfisher 15' bass boats they built back in the 1970s time line and only ran up to 70 hp engines...I had one. It didn't have stringers. It used a Balsa sandwich with FG on both sides....made for a cheap to build, lightweight almost flat hull for easy planing with lower HP engines......but rode rough as hell in any kind of chop. Was an ok material for decks as I know other mfgrs. of the day used it for that but not strong enough for transom punishment. Reason why I know that was because you couldn't mount your depth finder transducer inside Balsa filled hulls since it was soft and attenuated the sound waves going and coming.
On their Fiber Glass boats, I think most mfgrs replaced it and stringers with fiberglass honeycome or some other non rotting material way back there. I have a 1989 Ranger sales brochure (by Forrest Wood , Flippin, AR.) and he had already started using FG. His transom was called a Unique , stress-directed solid FG pulltruded unit. His stringers were reinforced FG and are completely glassed to the hull. Deck is 3/8" marine plywood (5 ply) FG coated and then a seal coat of Poly primer is then on that prior to carpeting.
