Permis de Construire for an abris de Piscine?

My parents have recently put in a pool and would like to enclose it in a conservatory .It already has walls on 2 side end of an outbuilding and the garden wall. I have looked up which permis but it's not that clear .

Déclaration préalable de travaux seems to be for up to 20m² of buildings but there do seem to be some exceptions. I found so info here

As the pool is small 6mx3m it may be possible with a DPT instead of a full Permis de construire but if anyone here knows more please do tell.

I wondered if the DPT would work as it will be a building without foundations?

I have no legal idea at all but surely it is a temporary structure (without foundations) so providing it's not a conservation area and a chat with the Maire should confirm what they would need if anything?