I have not worked with it, so I am automatically DQ'd from making any authoritative comments on gel. I just don't see how that stuff stays soft and gooey and still holds on to anything. I would try silicone caulk/sealant/adhesive first.
As to elmer's white v.s. yellow (wood) glue, I have never seen a glue failure with either. If you are worried about one of these being water soluble, I would point out that there are many other parts of the model rocket that you will have problems with first, if you get your rocket wet enough for the glue to soften.
I think the biggest problem with white glue is that it is not very easy to sand. It can be incompatible with a lot of paints (unless you primer it first) and cause crazing.
For me, the hands-down advantage of elmer's white glue is that you can buy gobs of it dirt cheap at the annual back-to-school sales. Pick up a dozen or two of those little bottles and they will last all year.