I yanked the fluorescent bulbs out of my 3 ThinLites and replaced them with these LED strips. I left the ballasts alone because I thought it wasn't worth the effort to remove them. They are no longer electrically connected.
Amazon has LED warm white strip lights for about $14 for a 5m (16ft) roll. They are 12V DC, and work perfectly for our vans. No transformers needed. You can cut the strips about every 3 inches to fit your project. I used the majority of the roll to finish out an under cabinet light project in the house kitchen, and used what was left over to do the SMB.
LED Wholesalers at Amazon
Amazon also sells strip-to-strip push-on connectors for cheap, but I used scraps of speaker wire and soldered the contacts to connect them together. You can't see it in the pictures, but I used crimp connectors to connect to the contacts on the original ThinLite switch. The strips are wired in series.
The LED strips have a 3M adhesive peel-n-stick tape on the back, and they stuck well to the bare aluminum, but wouldn't stick to the white painted ballast covers in the center of the fixture. Gorilla glue solved that problem.
Let there be (covered) light...
Although the ThinLite lens has a lenticular effect on the LEDs, the lights produce a nice soft illumination in the cabin.