If one uses peat moss to store tubers, you should not put them in cardboard boxes as the the boxes wick the moisture from the peat moss and then the tubers. Had you used peat moss in plastic bags and loosely tied the them shut, the moisture level would be the same as when you put them in the bag.
When you use vermiculite, normally you use no water as the vermiculite holds moisture(that is why they add it to soil mixes). The additional water is too wet for the dahlias. The most often used successful method to store dahlia tubers is vermiculite and plastic bags and no water. The next best may be wrapping dry tubers in plastic wrap and the next best is the peat moss, if you can keep the moisture levels correct. The same goes for wood shavings and again, one would not moisten the wood shavings, and you must use plastic bags. The plastic bags create a vapor barrier that keeps them from drying out if the humidity is low or rotting if the humidity is high. Remember that commercial growers store thousands of tubers every year. You should be able to store a few successfully.

PLASTIC WRAP SOUNDED CRAZY,BUT THIS YEAR I COULDNT LOSE! EVERYTHING ELSE FAILED IN YEARS PAST,AND I HAD THREE HUNDRED TUBERS SO HERES WHAT I DID
Gently lifted and imediantly hosed the tubers with a strong spray of water
HARVEST CAREFULLY BROKEN TUBERS GREET DISEASE!
SEPERATE LEAVING A PEICE OF STEM ( THATS WHERE THE EYES ARE AND NEXT YEARS PLANT COMES FROM.
DRY WELL THIS MAY TAKE A COUPLE DAYS THERE SHOULD BE NO SIGN OF MOISTURE!.
I USED A TOOTHBRUSH TO APPLY A POWDER FUNGICIDE SULFUR to the tubers coating lightly but well
Wrap snugly without harming stem ends wrap well!
Itd feb and my bulbs are doing AWESOME i check on them twice a month and have lost about twenty but whats great is the other bulbs arent affected since they are seperated!!!! So glad i tried plastic wrap lol!!!!

You used a toothbrush to apply a powder fungicide to three hundred tubers?You have a far higher tolerance to tedium than I do!