I use all different types of glues for what you're talking about. If it's a tight fitting joint, thin CA. If it's not the tightest fit I use med.CA. If it's structural, or a decent size gap, I use epoxy. For fuel proofing I use epoxy with a touch of denatured alcohol.

Walmart actually has a really good price on denatured alcohol in the paint department; I was surprised ($4.35?).