my truck is my "go to" vehicle as it is the most reliable one I own
so in light of that, then slowmover is correct in that showing how to use the truck as a single, do-it-all vehicle is what I am aiming for.
that said, I have a 94 mazda protege, 1.8L 5 spd w/o AC (factory delete) that I will also be doing some modification too, looking to get that well into the 40mpg mark. (rated at 33-35mpg as it stands now)
while I do use the truck for work purposes as well, 90% of the time its to drive to the job and back home, with the ability to carry materials. using an aerolid wouldnt hamper my ability to transport materials at all, as long as I allow it to be removable in the center area.
as for metal vs fiberglass, I have quite a bit of knowledge working with both, and I can promise that fiberglass would weigh as much as 2 times the aluminum to get the same rigidity.
I believe the screen would not be rigid enough for a belly pan, while I had considered coroplast, Im concerned with its longevity of life, I know the aluminum will outlast it by at least 6 fold, most likely more.
plus, as bob mentioned, I am more comfortable working with AL than anything else