I had the airline style bath in my 64 Safari. Dingy yellowing fiberglass. I took it all to Orange County Boat Repair, They Re-Gel Coated the tub, sink and trim. Shiny and smooth, could not be happier.
I have not used any of the epoxy tub and sink paints. However I have seen it done and the results are pretty darn good, and a lot cheaper than Gel Coating.
"Also, when I replace the flooring in the back what is the best kind to use?"
Subjective questen, however I say go with the best and forget the rest.
I used "Joubert Marine Plywood".