One solution is to just buy watercolour Blocks.... the paper is glued on all sides. This means that you paint without the paper buckling up on you. Then when you have completed your painting you just remove it from the block.
Here's an example of one of my watercolour blocks. There are plenty of makes out there, the one I'm using at the moment is a Matthew Palmer watercolour block with Fontaine paper. Incidentally the Fontaine paper is quite tough and can take quite a bit of work on it