Frank;
Three years ago I did exactly what you are proposing - for the same reasons. It was fairly expensive, but I ordered a 2' X 4' X 1/2" piece of polycarbonate from an online source (I think it was usplastics.com). Cut it on a table saw and finished it with a 2 HP router, using the original slats as a pattern. One note, tape the material heavily before using the power tools to prevent scratching.
The result is very sturdy (actually bullet proof!), watertight and looks great. The panels do scratch easily though, so you may want to consider vinyl storage bags. The 1/2" material is every bit as strong as as 3/4" teak.
It was also necessary to replace the vertical 'tracks' to accommodate the thinner panels. I made these from strips of 3/4" King Starboard using the table saw and router. I also added padeyes so that the panels could be attached to the boat to comply with the ISAF regulations for offshore racing.
Good luck with your project.
-Steve