Birch Butcher Block
I custom made some birch plank butcher block counter tops for our 1989 16er. The birch strips were from rough cut lumber, planed and fit together with biscuits, pocket screws, and wood glue. I think you could get away with only the wood glue, but because the camper will live outside in varying degrees of humidity, I wanted to additional strength of the mechanical fasteners.
Each plank was approximately 0.75" wide by 0.5" high. The butcher block is attached to the fiberglass via double stick tape.
As mentioned above, you can purchase butcher block counters readily from a home improvement store. If I did it over again, I'd just buy one and cut it to fit, rather than attempting to do all of the work to create my own. At the end of the day I don't think I saved any money, and I spent loads of time on this project. Anyway, it was at least fun to do.
We also have used some reclaimed oak from an old legal library shelving system to make the shaker style cabinet doors.