I did something like this when I built my one and only non classical guitar, ie; a steel string slide resonator similar to a dobro. I used a straight baffle to completely seal off the lower bout at the waist. The baffle had a 2 1/2 inch hole on each side with PVC tubes running through them. The tubes could be slid forward or back and locked in place with clamping screws. They could also be removed and replaced with longer/shorter tubes or just eliminated. The top was 3mm spruce with a large resonator cone inlaid into it. The client was a very advanced professional player and he was really pleased with the variety of tonal bias he could get from it. He experimented with tube placement until he found the sound he liked best.