I guess Yuet, the thing to do is get a good amount of plums, split them in half and remove the stones, then place them on wire rack - like a cooling rack, and place that in your oven on it's very lowest setting. I can't imagine how long it would take to dry them properly, possibly over night. I imagine the dryer they are, the longer they will keep. If the sun comes back out, you could try putting them in the garden in a super sunny spot, but you would need to put netting over to stop the wasps and flies messing about with them.
