I usually don't do anything with mine..
I just bring the pots/containers in..
and just stop watering them..
They're in a basement that's only heated by
the house furnace and two hot watertanks..
I also over winter believe it or not
one outside, on a south side, raised bed
with a cement sidewalk and a stonewall and
alot of mulch on top...
But I had tremendous luck and FUN with dahlia
seeds this summer.. what fun to have little baby
plants, and they bloomed..
Can't offer much more help on my end..
Can I ask when you said they were all shriveled up,
did you still try to
plant them?