Caravan on land with CU(B)

I am thinking of buying a piece of land which has CU (B) for a house.

What are the rules for siting a caravan on it please? It would be movable and not a fixture, just to live in for some months of the year until Permis de Construire is through and the house is built...

There is water and electricity to the site, but we would need to put in a fosse septique - would the caravan need/be able to be connected to it or does this render it fixed?

Mny thanks for info and advice!