Thank you for putting more thought into this than I did! :0

To wave my hands vaguely for a moment: I had imagined that the charge could be isolated on the *underbelly* of the tunnel and barge, simply with enough depth of insulator. And, by spraying the charges in a *vacuum* , as I recall, immense voltages arise relatively easily. I suppose the efficiency of generating those charges, and their duration *beneath* the craft, before migrating away, would be the main determinants of effectiveness. High current leakage also might heat the tube enough to melt it? :)

The image in my head, of a spray of charges on opposing plates, rushing past each other, squeezed by immense weight, *would* push charge - but how quickly? How far? With enough insulation, would the charges have enough time to migrate to the *top and sides* of the tube, due to the speed of the barge? [And what temperatures and currents would we see in the insulator walls, for a given speed and load? I am not certain it would be overwhelming...]

Also, I am not sure how like-charged plates would automatically 'decide' which of them would generate the *opposing* ionization you suggest. So, wouldn't it be possible to avoid your later '100x' voltage-requirement, by ensuring that both the tube underbelly *and* barge underbelly were *equally* charged?