I've found it's easier to hide a small-diameter, long vacuum reserve tank. I use a piece of 4" PVC pipe about 3 feet long with caps glued onto the ends and a grommet for a brake booster check valve fitted into one end cap. Paint the tank black and bracket it inside a frame rail. I prefer to run a second line from the tank to whatever vacuum accessories I'm using.
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!