The dome light got broken on my truck bed cover a where while back. I looked around for a good replacement but haven't had any luck. Eventually it got so bad that the bulb was too close to a wire and melted it so I removed the light. It sucks at night not being able to find stuff.
If you have 12 VDC in the Bed I'd used 12 volt LED rope light. I ran it under the Cover Rails. They threw away the Rope light at work after they couldn't get it to work. I plugged it in and had no problem. I bought the adapters and end pieces on-line.