Going by the setup of its undercarriage it could be possible to use a model tank of a branded name as part of the running gear, but i don't think it would be to difficult to build tracks from scratch, many of the scale tank boys do it rather effectively, as to water proofing its chassis i'm sure that could be sorted same way we do our boats, GRP skin or something around those lines.
Making it from lite ply would work quite nicely for everything above the tracks,, maybe some more durable heavy weight marine ply for the chassis 'box' in 8mm should do nicely.
I mean really its a very basic model to construct, the tracks would be the most complicated parts of it, but there are other vehicles without tracks, using over sized tires such as these...