There's enough room on the frame rails of most big rigs to hang a good-sized vacuum reservoir tank- - - -or maybe more than one. I like to use recycled Freon tanks. With a one way check valve between the intake manifold and the reservoir(s), there's enough vacuum for several brake applications. Vacuum wipers and/or an older 2 speed rear end can also benefit from having plenty of stored vacuum on tap.
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!