Hi Bob
Yes vacuum accumulators or reserve tanks work to a some extent, but it really depends on how much of the throttle you have to use to drive the truck. With my HUP the vacuum wipers work pretty well when I lift my foot or go to down shift, and because most of the time you drive that truck at about half throttle the wipers work. On my big C60S with the radio box when it had its original 216 engine the normal driving throttle was all the way on the floor or off the peddle completely you can guess the results no wipers or wipers.
I tried an accumulator can about 4 gallons, with a one way valve in line to the wipers the problem is how quickly you can store the vacuum and how quickly you us it. Connect the tank with the normal 1/4 inch line it really didn't work well. Connect the tank to the manifold through the 1/2 power brake port and the tank would work OK but not great.
I had the 4 gallon mounted on the C60S for a number of years for another purpose, I ran a small line 1/8 to the bottom of the clutch housing to scavenge the oil that leaked from the rear main. You could here this little hiss or slurping sound after you parked the truck which would last for several moments.
The best thing I've found is RainX with the reverse slope windshield it works better than the wipers do.
Cheers Phil
PS Changing to a 261 engine also works plenty vacuum.
Related Thread
http://www.mapleleafup.net/forums/showthread.php?t=6896