FOR YEARS TO COME…
You will receive your hut with pre-treated floor joists to make sure it does not get affected by the raising moisture from the ground.
Without any additional treatment it should last a decade; with - double that.
As long as the hut is lifted a little bit off the ground / is not standing in water, it will last a long time without any treatment. Plus, overhanging roof protects well the timber structure underneath.
However, in order to further extend the lifespan of your ETT, our advice would be to treat it with natural, petrochemical-free materials.
The first step would be an anti-fungal, anti-rot treatment.
The second step would be treating with a natural oil. Such as linseed or a linseed oil based paint, which protects the wood from the moisture, is breathable, does not create a layer on the surface, and if you decide re-apply it a few years later, the remains do not have to be removed and can be just painted on the top.