Over the past 2-1/2 weeks I've been through the mill re. coroplast construction techniques. I built a temporary air dam using a full 4' x 8' sheet; this was a large and somewhat heavy project which really taxed my assembly skills. So I think I'll share some of what I learned.
1) Clear duct tape by 3M is not what you want. It gradually lets go, allowing your construction to come apart. 3M also has a bargain brand of "regular" duct tape, also to be avoided. "Tartan" brand, I think? It's quite thin and tears easily. Most average or "pro" grades of duct tape are probably OK.
2) Pay attention to the direction of corrugations and which way the stresses will likely be. If you need a long piece, you still want the bend-resistance in the right direction so you might be better off joining two pieces together if for example you need a 6-foot piece and your stock is 4 x 8 feet.
3) For joining pieces at right angles - as in a vertical-face air dam with an attached belly pan - I can highly recommend a strip of "corner bead" sold for joining wallboard at corners. It's angle stock, made from vinyl, very strong and lightweight; ideal for coroplast. Get the curveable type, used primarily for arches. Has notches at one-inch intervals so it will curve where you need it to. About $2.xx for a huge piece maybe 10-12 feet long at Home Depot etc.
I first used the corner bead with only duct tape but found it needed stronger attachment at some points. 1" x #6 wallboard screws worked perfectly, but you need a thin wood strip on the backing side for the screw to bite into. And of course duct tape also. I taped over the screw heads when done, just in case any start to back out one day.
Note that I used the corner bead behind the front face, but underneath the horizontal sheet. See the tape on back side of front face. Afterwards when you add tape on outside of front, you can push on it and it has some resistance.
The pic below is a bit small for this detail - but you can maybe see that I layered and staggered the duct tape. So the result is that it's thicker and wider than it was when made.
See the drawing below.
[hopefully it's visible to all now]
Coroplast is black outline, corner bead is heavy blue, duct tape is gray, screws are brown. I didn't show the wood strips that the screws bite into but you get the idea. Lattice strips or louver slats should be fine, about 1/4" thick.
Heres a pic of the air dam:
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.
I'm not able to see the photo for some reason. Maybe my work computer doesn't allow it.
I used Gorilla Glue on my front undertray and it is still solid. I would recommend it for anyone trying to do something more permanent. I'm not saying you should have changed anything, just that Gorilla Glue worked for my application.