A couple of questions about dahlias and rhubarb

I'm a novice gardener so I'll be searching for a lot of information so apologies in advance.
My first issue is that I'm not sure what to do with dahlias and rhubarb

1 The dahlias are still flowering but we will be away from the middle of November. Should I cut them back before we go as the temperature is supposed to drop
2 I've had conflicting views what to do with the tubers (we live near Birmingham Uk) one view dig the tubers out wrap them in paper and put in a garage or cover them with a thick layer of mulch . Which do you prefer and why

I've just received some rhubarb crowns I wasn't expecting until early next year. I can't plant out as their home isn't ready what can I do to keep them until spring next year