You can try to plan the sequence of joining the parts so that seams will be felled.
But I always find there are some that can't be done that way, at least not handily.
So, french seams with the edges covered by binding is what happens. You can use something heavy, like grosgrain, but I find nylon tape, like the cheap tent companies use on their french seams, is fine. The purpose is to protect the edges, not reinforce the seam, except in so far as the additional line of stitching reinforces.
Made a pack a few years back and fretted about not having it all flat felled seams.
In actual use, never even noticed. Had to go back and look at the inside of the pack to recall what was not flat felled.