I have seen this in crocodilian holding tanks at zoos but don't recally seeing a large adult of any species housed this way. That does not mean I didn't see it.
Having experience with both pond liner and keeping crocodilians, my biggest concern would be keeping the water clean with all of the folds in the liner. Unless you built a wooden form and had a hot tub company make you a perfect fit liner, assuming that process still exists. Years ago hot tub companies could make a form from lumber and plywood, complete with steps, sloped sides, etc. and then make a liner that would fit perfectly.
Still, this would not be my preferred way since you'd still have to sump the water out of the tank. If I ever keep crocodilians again I will absolutely require an easy to use bottom drain for the water portion of their enclosures. They are just too messy otherwise.
I would ask this on the croc forum if you have not already.
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Current snakes:
0.0.1 Gonyosoma oxycephala - Java locale (green)
1.2 Gonyosoma oxycephala - Jave local (green)
2.2 Gonyosoma janseni - Seleyar locale (all black)
1.2 Gonyosoma janseni - Celebes locale (Black & Tan)