how to keep kappa-carrageenan lasting at room temperature for weeks or months? (art project)

I'm helping an artist make an outdoor gelly structure (not for eating) and we want to keep it from molding. The temperatures are around 10-30 degrees celsius and it's in Copenhagen, Denmark in September, and hopefully, it can last for some weeks or more.


Right now we are experimenting with kappa carrageenan with a mix of CaCl2 and we are going to add locust bean gum, pectin, and sugar to see how it behaves.
But what would we add for conservation? Sodium benzoate? and is there a limit on how much to add? (we want it as transparent as possible)
We don't wanna use some too harmful chemical since we gonna have to get rid of it and work with it.


Thanks, any help is most appreciated. Have a nice day.


Resources I found so far:
In this paper, they say they can make it last 7 months at room temperature.
The paper mentions Potassium makes it last longer:
<https://idosi.org/wjdfs/wjdfs6(2)/18.pdf>


food exchange:
<https://cooking.stackexchange.com/questions/57752/how-much-citric-acid-to-use-to-preserve-vegetarian-jelly>


general booklet on caragenan:
[http://www.bisi.cz/cmsres.axd/get/cms$7CVwRhc3USVqgzxkKF96gI$2BChNrXcTq$2BOUdiEtz5TfYA$2Fg1ADRHMfXfdEjUsYQagqUs9N6byPOkok$3D](http://www.bisi.cz/cmsres.axd/get/cms%7Bb914bcb4-5f6b-4e51-9c8d-2da1ca475172%7D2BChNrXcTq%7B666e580c-4d58-4ef1-9a6d-cd3f5700b6fe%7D2Fg1ADRHMfXfdEjUsYQagqUs9N6byPOkok$3D)


