In your situation I would try:
1) Take cuttings of any particular favourite plants, you should easily get 5 cuttings per 5 inch half pot and keep them, frost free and just moist, on a window sill over winter.
2) Try inverting a plastic plant pot over the plant in the ground and cover that with leaves. I would avoid plastic sheet as I would be worried that plants might rot if there was no way that the plant could 'breathe'.

Thanks!

Andi....the crawl space might do enough if ....IF that place can be kept cool...not cold...not warm...just cool.
You definitely do not want moisture to touch them....
drier is better.

If this is the case, then you can place your plants into a cardboard box that you place newspapers in to serve as a bed.
Before storage, after you dig them up...remove all the old soil...remove any damaged stems, remove all the old leaves....but DONT cut back at this time.

Into the box (newspaper bed), and cover with a drying medium...peat moss, vermiculite or dry sand.

No light should touch them....no warmth should touch them...no moisture should touch them.

CANT do that...do you have a shed or garage....or
does a neighbor have such a place to keep the plants.

Normally, a garage or shed will be as cold as the outdoors...but you can take steps to insulate a cardboard box against the freezing temperatures. Styrofoam makes a great insualtion....and if you can pack a sizable box with sufficient styrofoam, then pack your plants in it, then cover the box with burlap and anything else you can think of to keep the contents from freezing, the plants can survive such a storage.
But, they must not freeze.

ARound mid February----the sun begins its slow travel up north...it is then sufficient to initiate new growth.
Bring the plants out, cut them back now...to about 4" to 6"...remove any old soil and leaves and broken stems.
New potting soil---put shards into your pot...a 6" or 8" pot will do nicely. The shards in the bottom of the pot to keep the soil away from the drainage holes.
You can, if you like, mix the potting soil with some sharp sand and/or peat moss.

Into the pot, firm it up....and water til it drains.
Then to the best window you have....but north at this time will just not do....east, south or west exposure is best.

Don't water again until new leaves form...and turn the pot 1/4 turn every day...or so.
Don't feed until new leaves form and then at 1/4 rate.
Keep the soil surface damp...but on the dry side between waterings...and when you water, always water til the pot drains.

In about 3---5 weeks, you should see leaves forming....the buds will show first.
In maybe 2 months, new flower buds.

If you use such a place such as a garage....if you can hook up an incandescent bulb to shine down onto the plants in the box...during nighttime cooler temperatures, it might be enough to raise the tmeprature above freezing.

That's it....you can keep your geraniums going for years and years.