Outdoor extension cord that can be left unplugged?
When I was in a colder climate and needed to plug my car into a block heater at night, i installed an outside outlet with a water proof cover and put an external rated gfci outlet in it.

That way, the extension cord could get plugged into a water proof outletand if it were to short against ground, the gfci would trip. I hung the other end of the extension cord when not in use so that the plug pointed down towards the ground so it would let get ice or snow in it. 

Surprisingly, the outlet never did trip over many winters. Snow isn’t conductive and pure rainwater isn’t either, but if there was a short to ground you had the gfci watching your back. You could also put a switch on the  outlet — either a waterproof one outside or a switch inside, so that you could shut off power when you wanted to. 

In any case, my experience was in a cold clime. You may want more protection in a wet climate. Or your wife might want to look at self enclosed battery systems or generators to maintain power to her equipment. GFCIs can trip and your wife would lose refrigeration to her truck if she doesn’t have battery backup.