There are two parts to the answer of this question. The first part: No, that really wont work so well. Vapor barrier liners work by reducing evaporative cooling, the cooling that comes from moisture on your skin as it, well, evaporates. So you need that layer very close to your skin, not outside of the bag. The proper sequence would be: Youre inside the vapor barrier liner, the silk liner goes outside of the vapor barrier liner, and then the bag goes over all of that.
The second part: Do you really think you need that much stuff? It does get cold on Kilimanjaro, but nighttime temps arent going to dip much below -10 C (15 F). Most any good three-season sleeping bag, maybe with a silk liner, should be adequate for that. Marmots Helium (US$359) would be perfect. It weighs just under two pounds, has 850-fill down, and is a good-fitting bag. The silk liner would take that down to -15 C.
Up your way, MEC sells a house-brand bag called the Merlin (C$260), a -10 C bag that has down fill and a stripped-down design for light weight (33 ounces, so a touch less than the Helium). Nice bag!
Hope you have a good trip; everyone who goes loves it. Just take lots of hand sanitizer.
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