I'm not sure if I completely understand, but you could mimic something like what is done with faux stucco finishes over styrofoam insulated concrete forms.

Instead of a stucco finish you could apply a thick layer of latex drylok and then lay down a layer of polyester mesh tape while that first layer is still wet. Then put on a second coat and it should be plenty strong.

I only mention latex drylok because it is cheap, waterproof, safe and readily available in quart containers. But there are probably other choices as well. And I also know for a fact that it sticks very well to styrofoam.
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Currently keeping:

6.10 Gonyosoma oxycephalum (Javan, mixed colors)

0.0.4 Rhynchophis boulengeri

1.1 Philodryas baroni

1.1 Lampropeltis triangulum multistriata

0.0.1 Rhamphiophis rubropunctatus

0.0.2 Morelia viridis (Aru & Merauke locale types)

1.0 Rhodesian Ridgeback

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