Cague, you don't say where it is you live...so let's assume its a zone 5 or 6 area and you cant grow your pelargoniums outside year round but must bring them inside before being hit by frost.

Forty plants...that's a lot of color...a lot of plants to deal with. You'd have to have the space indoors to properly keep them going through winter.

What is more important is the sunlight that the plants must have and round about mid October through until mid February, the sun's values are much diminished.

So that brings about how to save them.

The usual method of cutting them back prior to bringing them in and placing them in the best window you have...south, east or west is OK....north...wont do.

Keep them going as they will and let them grow until you can use them for cuttings. Or take cuttings right away.
If placed in smaller pots (3-4") after dividing, they are kept going until new roots and new leaves form when you can then re-pot into larger pots...(5")
I keep thinking 40 plants...divided...so that's at least 80....80 pots in windows...and more if you take cuttings.

The method of placing them in a cool basement is not available for you.
Let's assume your garage is attached to the house.
The wall next to the house can be 3 - 5 degrees not so cold as the space outwards.
If you have a shelf there...it'd have to a big shelf for 40 plants.
Boxes....cardboard boxes into which you place styrofoam on the sides and bottom, Then place your plants into...then surround with styrofoam, peat moss, sand or vermiculite.
It must stay dry.....dry, cool and dark.

Around the box you place a large plastic garbage bag...enveloping the whole box...then surround that with burlap. This should be sufficient to keep the plants from being touched by frost. The plants must be in a dry state before going into such plastic bag. Moist plants, placed in a closed bag (especially plastic) will certainly be in jeopardy due to mildew and/or mold.

Further, you can arrange a light bulb...s bare light bulb above the box/es to turn on at night during the coldest times. This can keep the area warm enough to shrug off any inteseness of cold.

This sounds to me like a lot of work for all 40 plants...but if you can provide for them, you should be able to bring them back for next spring.
Mid-Febraury, the sun begins its travel back and this is the time growth can be initiated. The plants would come out of hibernation and, cut back, re-potted in fresh potting soil, watered and given the best sun.

They then go back outside when you plant your annuals.