I used the tried and true double glue method when I started in rocketry back in the early 70's. These days, I use thin CA glue to tack each fin in position - the smallest of drops is all that's required to set a fin in position. If I get one on wrong, it's a simple matter of a little leverage to "pop" it off and try again - though I use one of the simple yellow Estes alignment guides, so that doesn't happen very often. I can get them all tacked on in a couple of minutes and when I'm satisfied with their alignment, I drip a bit more thin CA into the fin-BT joint to get a better bond along the whole edge. Finally, I finish up with a fillet. Again, in the interest of time, I use quick set epoxy, but traditionaly wood glue fillets are fine if you don't mind waiting.