Not sure you're going to get away with not using fiberglass on this, along with the PVC. I've seen a custom setup that used PVC tubes to mount the gauges into but the rest was 'glassed in and then sanded/painted to match. Looked really labor intensive.
I cheaped out and got the A-pillar mount. Much easier plus I can run all my wires right up the side and not mess with the dash area.