[jrblasde]

My gut feeling is that the automotive gasket paper would be adequate, but I hesitate to provide a definite "yes". Gasket paper has a similar composition to fish paper (i.e., it is a fibrous material which is impregnated with rubber), but the manufacturer intends for it to be a pressure seal with good thermal insulation rather than electrical insulation. Thus, I doubt that the dielectric strength per mil of thickness has been quantified.

Now that I know that the purpose of this paper is to shield against accidental contact between the can (which is tied to the chassis ground) and its inner components (connected to B voltage), that's the only reason I hesitate to say yes. But, you can certainly run a test! You might try using the high voltage output of a transformer, with an ammeter in series. Do not short circuit this setup, but rather place a piece of your automotive gasket in the circuit (transformer high voltage -> ammeter -> gasket paper -> return to transformer). Make sure to press the leads onto opposite faces of the gasket paper. You need to be making secure contact with the paper, so tape the leads down to it. Energize the circuit and let it run for 10 or 15 minutes under supervision. If it is adequate for electrical insulation, then you should see no measurable current on the ammeter and the gasket paper should show no signs of melting, burning, or darkening in color. If it passes the test, then I'm sure you're fine to use it for this application. Just don't do it for commercial purposes.

This is all coming from a transmission power engineer, so I am likely providing worst-case insight. We must be very careful about insulation and grounding at those sorts of voltages.