For something a little less permanent,you might go get a roll of that static cling window tint.You could cut a piece out that would protect the tank from your belly,then just peel it off when you don't want it on there.You can use it over and over.
My nephew uses a little square of this stuff on the rear fender of his H-D when he has his sissy bar bag installed.It hangs down just enough to rub on the fender.
I've got a strip of it in my jacket pocket that I can stick across the top of my face shield.Sure makes riding into the sun a lot more pleasant.

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Cheers!
Bruce