How can I prevent watercolor paper from buckling?
To prevent the paper buckling/cockling you pre-stretch it, That is you wet the paper and tape it down to a rigid board with gum strip. I generally use a wooden drawing board that I made in work shop practice 50 odd years ago. Note masking tape does not work as well as gum-strip for this as it does not adhere very well to wet paper.

You paint onto the stretched paper and only cut it free from the gum-strip when finished.

Heavier paper (say 300+ grams per square meter) usually does not cockle when you paint on it using water colour technique (do not regard this as a challenge, I'm sure you could get it to cockle with a wet enough technique).