I am located in Portland, OR (USDA zone 8b). We have cool, sometimes cold, very wet winters. The nights don't all that often go below 28 degrees or so, but there is always that one or two weeks where our temps dip into the teens for several nights.

I have very limited indoor space to overwinter beloved tender plants, but can manage to put some summer bulbs/corms/tubers into a box of peat moss or vermiculite in a small unheated basement area.
But I can't put everything I'd like to in there.

There are a number of tender bulb-like plants that usually, though not always, survive if left in the ground. Dahlias, for example: some live, some die.

This year I grew a really nice Colocasia Elephant Ear "Fontanesii", which is said to be one of the hardier varieties of Colocasia--some say to Zone 7. This plant sent shoots out all over and many took root. Woohoo! I will dig up one or two of the tubers to store in the basement with my caladium and begonia tubers, but will leave the rest in the ground to fend for themselves.

I'm OK if they don't survive, but to give them the best shot, here's my question: I know I should mulch them heavily, but will they fend better if I were to cover them with a plate or board to reduce the amount of water that gets to them, or to just let our massive amounts of rain have at them? I fear they are more inclined to rot than freeze. I'd appreciate any thoughts about this. and based upon answers I receive, I may try the same with my dahlias.