Court. Sorry for late answer.
I think it's reflective tape but that relies on another vehicle light source
Won't do much for required side marker light.
If you take your existing rear tail light lenses and have a shoulder built up all around it and your clearance/running tail lights are to the outside then a couple of longer mounting screws should suffice.
This is better than side marker lights as it also displays the rear ending of your truck for approaching vehicles from the sides.
Most acrylic fabricators find making a car part a refreshing challenge and relief from making magazine and pamphlet stands.
Inexpensive too. The set for my wife's commando cost $20 CAD.