If you want a little safety margin, find a 30 lb. Freon drum and mount it somewhere out of sight, under the bed, etc. and run a 1/2" diameter vacuum line to it through a 1-way check valve. I just use a regular brake booster check valve and grommet, fitted into the blowout safety cut in the tank with a Dremel tool. A little strap steel to mount it, and you've got a vacuum reserve tank big enough for 2 or 3 brake applications even with a dead engine.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!