I had a box without cover, I just designed this and attached a bematik outlet so I can use additional external plug to the wall.

This is the outlet: https://www.amazon.it/gp/product/B07NW282YV

This is abox similar to the one I have: https://www.amazon.it/Poly-Pool-PP0585-derivazione-92x92x45mm/dp/B091HQD1K5