Another option:
I use stainless tee-nuts and button head socket screws (5/16" x 1/4") to fasten the upper/lower shroud sections together. They look good, allow for quick separation of the shroud halves and are easily reassembled.
Remove the shroud halves from the truck and clamp them together - the guide pins with maintain the correct line up.
Drill 3 appropriately sized holes (to accept the OD of the threaded body of the tee-nut) through both flanges. As far as locations - I use the same spots as where the factory staples are located.
Un-clamp the shrouds halves and set the upper aside.
Thread one of the screws into the tee-nut (provides a place to hold onto with some Channelocks).
Apply heat to the tee-nut with a torch - until it is hot enough to melt into the plastic of the shroud. Line up the tee-nut with a hole and gently sink it into the upper surface of the lower shroud flange.
The 4 claws will sink right through easily. The trick is to apply just enough pressure so that the round upper surface of the tee-nut will also become just partially embedded into the plastic.
It takes some practice to learn how hot to make the tee-nut. If it's not hot enough, it won't melt/penetrate/embed in the flange. If it's too hot (and you push too hard) you can push the entire tee-nut right through the flange.
When all the tee nuts have been inserted, use a pair of Channelocks to bend each of the claws over. Do this with the jaws of the pliers on the face of the tee-nut and the claw point. Squeeze the pliers until the claw bends over onto the lower surface of the flange. It isn't necessary to do all 4 claws - there will be one that is difficult to access.
When you are done you will have 3 permanent threaded stainless inserts in the flanges of the lower shroud.
These images are all I could find of the finished product:
