Apparently the product supplied by Bostick & Sullivan is a roof patching product called Elasto-seal. Normally comes in a huge can from the hardware store. I have to patch some holes in my Kodak 2d - I'll look into the E6000 product. I looks like Michael's craft stores carries it.
Book binding tape. Flexible, archival (supposedly), designed not to crack or break over time. Probably will leave a sticky residue that may or may not be removed with a solvent. I believe it's available in cloth and linen.. I'm not talking about the clear stuff or paper tape used to repair pages, i'm talking about the stuff used to bind books and repair bindings. Pretty handy stuff, not sure just how different it is from gaffer's tape, except that it is probably thinner and comes in a lot of pretty colors.
E6k sounds good too, as well as plastidip and the roof sealing stuff. I'd go that route first, unless the bellows are torn and ripped up. In which case i'd probably tape away. I've always heard of using acrylic black paint mixed with elmer's white glue.. Lots of different ways to do the same thing.
I use 3M polyester tape type 850 black. This tape is so thin, 0.05mm, that it does not bulk up the bellows even if you covered the whole thing. The tape is very flexible so it can be used to patch pinholes in the corners and then the bellows can be re-pleated easily. Best of all the adhesive is strong, doesn't bleed, doesn't creep, and never goes gooey.
The downside? It is an $$$ expensive roll of tape.
Gaffers tape is expensive, but it takes me years to go through a roll. I wind some on to a 120 roll film spool and keep it in my camera bag, very handy to have. Can be removed from most surfaces without leaving residue. I just bought a 5x7 Kodak D2, I have to check the bellows for light leaks. I'm inclined to try the E-6000 for any pinholes. If I had a tear to repair I wouldn't hesitate to use gaffers tape.
This is an older thread but I'll put in my 2 cents. Black bookbinders tape works very well on most any type of bellows. We not only used it to bind books but to repair holes/tears in the bellows of the big process cameras. Once stuck it never comes off and remains very pliable.
I'd be careful with gaffer tape. I've used it for temporary fixes (like attaching lights to whatever is available when there's no room for stands), and I've noticed that if you leave it on for a short while, no more than a week or two, it leaves no residue. But if you leave it on for several months, it does -- thick, sticky goo that's very hard to remove.
These people sell black liquid neoprene rubber in a 4-oz brush-on can. I've ordered some for bellows pinholes, but haven't tried it yet. It's actually manufactured by the Plastidip people and re-labeled by these dive shop folks as "Trident Neo Coat" (found that out by reading the MSDS sheets). Plastidip sells the same product but calls it "Liquid Tape". It even comes in a spray can (from Plastidip). Be careful about ordering liquid tapes and such, many are just a plastic vice rubber compound and won't be as flexible or last as long. This stuff is supposedly liquid neoprene rubber. http://www.dolphinscuba.com/ProductDetails.asp?ProductCode=AC_LP55&click=287