Danger! Danger, Will Robinson!!
DO NOT use Plastidip, liquid electrical tape, or similar on a bellows. I did it once, on a Wirgin Auta with a lot of leaks at the corner folds. Good news is, it stopped the light leaks. Bad news was, the first time I tried to close the bed, the bellows stuck together and it took me a half hour or more to get it open, and even after dusting it with talcum powder (which looked great on the black bellows) it wouldn't fully close due to the extra thickness. I wound up stealing a good bellows off another Auta that had a less desirable lens (i still have and use the repaired camera, and can see the slight misalignment of the new bellows when I shoot without the format masks).
I've had much better results with black masking tape (applied both inside and outside) or the thinnest latigo leather, dyed black, and applied outside only (both of my Zeiss Ideals have a number of leather patches; they're almost invisible, not so thick, in reasonable numbers, as to affect folding, and even though they're only stuck on with rubber cement, they've now held for fifteen years or so).