Semi Truck Fiberglass Day Cab Conversion Kits. No need for your semi truck sleeper any more, no problem. With a Big Rig Day Cab Conversion Kit, the transition is easy. There are many kits to choose from to transition your Semi Truck Sleeper into a Day Cab. Extended Day Cab Kits offer six additional inches of leg room for driver comfort. This kit quickly replaces the existing semi truck sleeper with no modifications needed to the factory cab or interior. When you consider the ease of installation, combined with the rapid turn around time, this kit is the perfect solution for your semi truck conversion needs.