Hmmm seems more like a solution looking for a problem where the correct answer seems to be GET AN ELECTRIC TONGUE JACK. Be careful of the save a dime and cost yourself a fortune with a healthy side portion of grief syndrome.
I also like the idea of keeping the 7way plugged in when using the electric jack for power and I do the same when putting my slide out before hooking up to the pedestal, but I have to have the Van running or it can take A LOOOOONG TIME to get the slide in/out just on battery alone.
Larry