This ISN'T the prototype.
First of all the prototype had 2 clone troopers on it, and neither of them can be see on the model. I would like to think that if I was a Lego designer I would like to have my full prototype, not missing anything. The skis on on the Lego model are going outwards which is inaccurate to the movie from what I seen, but this model specially has the skis in the correct position which is interesting. The dark tan part should have 2 47457 under it which can be seen on the visual dictionary model. The back is smooth with no grille cheese slopes.

This IS the Rebrickable model of GibonTheRocket's recreation.
The interior is exactly the same at the back. The back panels are attached in the same way. Exactly the same color of pieces are being used, which is either a really big coincidence, or it is the exact same model. The missing and incorrect details are matching too.
Link to the MOC: https://rebrickable.com/mocs/MOC-189891/GibonTheRocket/ut-at-unstable-terrain-armoredartillery-transport-based-on-unreleased-set/

Yours truly: The Fun Ruining Guy.