I inadvertently hijacked John's thread about spar-to-side fastening for the headliner, so here's how I do things with dowels, not pocket screws. I mentioned that I don't own a pocket screw jig, but here's what I use for most of my building. Basically, a layout stick is used for building cabinets in a custom shop when I apprenticed in the early 70's. This provides all marks & measurements for panels, dadoes, face frames, drawers, doors, backing & all of the parts needed for building a finished piece. I've heard people say "It takes too long to do a layout stick" but in reality it helps track materials & cutting lists efficiently. Drawers are made with dado joints, similar to the way the side walls attach to the bottom of our teardrop. Fasteners & glue are used to pull the joint together from two directions.
My doweling machine from the early 70's. It's a 1/4hp motor with a chuck, brad point drill (1/64" oversize), sliding table with a 1" slot in the fence for hole alignment. It's pretty crude, but actually works well enough for production.
Here's the tick marks & X marks to track hole positions. These are just transferred from the layout stick to the face frame stock, then drilled with the boring machine.
With dowels placed, glue would usually be in first, then clamps are set. Yes, you need clamps to make tight joints with this system, but it's bulletproof structurally.
The two questions I ask;
1 - does it look good?
2 - did it hold together during use?
Here's a dowel joint I did yesterday. Red oak is ground to make a tight fit in the tapered spear head. West System epoxy & a screw holds it in place. It's theme & variation, ad nauseam, just a different type of dowel joint. There is no right way to build, just better, more efficient & stronger as practice turns into production over time. Note: I did not use pocket screws to make this spear!