Gluing and clamping long miters

For "edgebanding" plywood by cutting off 3/4" at a 45 degree angle, then turning it around and gluing it on the end, I wind up with a long (and somewhat warped/twisted) piece to miter

Anyway, I just put down a sheet of polyethylene over a flat surface and lay it down (usually it's a shelf) and clamp it down along the edges, slather glue in the usual places, and clamp them both ways (slowly tighting each of them so one doesn't overpower the other). Any gaps get another clamp.

Since the edgeband piece's point is basically getting clamped down into the workbench, you have to be careful not to crush it though, and the fir is pretty soft.

The polyethelyene will prevent it from stick> I've got a number of long miters to glue-up shortly and I'm hoping to

I join the miter to give myself a leg up. Seems there's always a problem with mitering over any length on a tablesaw.

Last set of carcasses I used the L outside, 2x2 inside. Making the outside one sturdy is what I consider key. It's got to exert pressure evenly over a distance. The legs of the L meet at ~85 degrees and are overcut on the tablesaw -blade's higher than the fence distance- to create a little extra pocket where the tips of the miter can slip without crushing and glue ooze without sticking, though if I do it again, I'll wax 'em. If you're doing more than four, you should.

If the distance is excessive, even that might not be enough, so you might have to go to clamping one piece to the table and wedging your supported other piece along your caul/clamp. Plan "A" seemed to work all right at