It's beena long time and I can'trecall specific brands, but I think there are various waterproofing compounds that will work on paper. These days follow kenK's post and just order your map on waterproof paper.

I did a cursory search for the map tape I used and came up empty. But it was a sturdy tape that could be folded indefinitely (my maps lasted for more than fifteen years with a lot of use).

The thing is that if you simply fold a paper map, eventually the paper will wear through, obliterating some of the info on the printed surface. There is some natural law that decrees that you will need to look at the spot now worn through. Cutting the paper cleanly and inserting a hinge solves the problem.

This is worth the effort if you are going to use the maps a lot.
Geezer in Chief