Blue buckets?? Just add A few full spectrum lamps and grow some Geraniums or something.
I’d leave the door open and see what was happening above / below the cupboard ( outside walls, guttering etc but especially above ). Water doesn’t just creep out of the ground more than a few inches. I live in a damp valley and we had the back windows properly sealed, ran the down pipe 10 feet into the garden and dug a large French ditch with underground run-offs into the garden.
A house won’t be damp without water ingress. Check your gutters, run an eye over your pointing, borrow a ladder and inspect your roof tiles. If your house is damp it’s getting in somewhere from above, I promise.