No matter what the Chevy Duty rep said, the Shop Manuals say to set the tape and glass in the frames dry. If you have the correct thickness setting tape (and glass), the dry fit should be tight enough to hold the glass in place. After "wetting" the tape with oil and leaving it overnight, the glass should be set (and not move).
Chevy Duty used to sell two thichnesses of glass setting tape. One supposedly works with the side glass and one works with the vent glass (depending on the years). I found that they sometimes sent wrong thicknesses of tapes and I gave up on them (and Jim Carter) sending the correct tape.
Restoration Specialties has four thicknesses of "grip strip rubber and cork (impregnated with ground talc, as original)"
glass setting tape (page 29). I bought one roll of each of these tapes and had no problem setting the eight panes of glass on my suburban and a vent and side window on my pickup. I needed to use three different thicknesses of tape.
Restoration Specialities is an excellent company and the people who answer the phone (usually the owners) know what they are doing (and they have been doing it for 30 years). Their catalog is incredible (on-line or $3.50). Whether you are doing an authentic restoration or a modification/restoration they have correct hardware and trim parts that are not available anywhere else (and scale-sized pictures in the catalog). Oh yeah, they have the channel fasteners/clips that it seems that most vendors are not supplying anymore with their side-window channels (page 27 of their catalog).
Sorry about this rant. With the correct setting tape, correct glass thicknesses, and correct techniques setting glass is not a hard undertaking (and modern silicone-sealant is not needed).
Shooper's technique works and Laroke's/Hedgehog's suggestions sound great (I wish I had seen that before I did my last two vents).
Good luck,
Tim
