Funny you should ask.

There's a flat plywood sheet going from the bottom of my air dam extension back to the oem plastic belly pan.

I made this one out of approx. 1/4" plywood. I hope to redo it this spring out of 2.7 or 5.4 mm. lauan plywood, from Home Depot and most such places. Prime with oil base house paint primer, then topcoat with Duplicolor black pebble grain pickup bed liner. That's low cost, only about $7/can. Flexible plastic for the side pieces; best I can recommend is 5 gallon black buckets (like for paint or spackle). 18-wheeler gear lube comes in black plastic buckets so try a commercial diesel service shop. I used white buckets; paint keeps peeling off.

See the related discussion threads at
http://www.gassavers.org/showthread.php?t=3608

On that board my handle is "brucepick"



--
Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.