Hi I need some help.

I am wondering if anyone is familiar with the brand Das Pronto Modelling Material?
I would like to use a modelling clay at the bottom and up along the back wall of my tanks for my leopard geckos. This particular clay air dries but it doesn't say on the package if its toxic. Does anyone know? I need it mainly to fill in gaps between the ceramic tiles and the side walls of the tank, but i'd also like to create holes where the food/water bowls go as well as imbed some plants into it.

Also, is there a better modelling material i could use? Do i need to cover the material with some sort of nontoxic varnish?

Huge thanks for any help
Red
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Crested Gecko Zeek:1.0
LEOS: Boo: 1.0 normal , Bronx & Nala: 1.1 blizzard,
Lily: 0.1 patternless, Abby: 0.1 albino, Zoe: 0.1 reduced pattern, Dot: 0.1 hypo
Chip: 1.0 papillion (small dog)
2.0 bettas