Love the idea of the dowels. Maybe I’ll cut and move my 2x4 in between my vertical posts (so that it doesn’t extend forward at all. And then just use the temporary dowels as you suggest. Do you secure your work piece with clamps or screws?
What I’ve always wondered about skirts: how do you plan to use materials with different thickness? Do you imagine you’d have additional spoil boards of varying thicknesses you could put behind your work piece (if you want to cut 1/4" board for example).
Edit: here are some pics of my frame.