Evaporating Gas

Just got the white princess out from storage yesterday.
Six months ago when it was put into storage, the gas tank was FULL.
Glancing at the gas guage while driving down the road, I noticed that the needle
was barely pointing to 3/4 Is it possible that over 1/4 tank of gas evaporated
during the 6 months of storage??? I have to wonder about that

That sounds a bit suspicious to me. From what I know about fuel systems they're a pretty tight closed loop. I haven't noticed any loss of fuel over the past two winters that I've owned and stored "The Toy". A loose connection somewhere in the fuel system or a bad gas cap seal would be the only things I could think of that would allow that much fuel to escape. Was there any kind of fuel odor in the storage area near your car? Or any evidence of fuel on the floor under the car?

The only other thing I can think of is someone at the storage place needed some fuel and helped themselves to a little (unless you have a locking gas cap).

Didn't smell a fuel odor. The storage facility has a dirt floor with a thick covering of large shale.
If any gasoline leaked, I imagine the white shale would be a bit discolored but I really didn't notice. It's parked in my garage now so a leak would appear on the floor; I'll keep a close watch. Looks like I'll be investing in a locking gas cap...

Yes. Gasoline can evaporate over the winter, especially if winter humidities were otherwise low.

Hi
Did you physically check the fuel qty.
Indication systems might show erratic wrong qty, specially after long storage with possible water condensation or bad fuel.
No way, 1/4 of your tank has evaporized.
Hey, I'm looking for a locking gas gap already for a while.
I need the big size cap for eraly C3, tank hole is about 3 inch, cap about 3,5 inch diameter.
Any idea about aftermarket locking cap ?
Thanks Gunther

The gas gauge being wrong was the first think I thought of. To verify the tank was only 3/4, I stopped at a gas station and watched the number of gallons it took to fill. 1/4 tank of gas was pumped !!!!