I had a similar thing happen to my countertop in a small area by the sink. I clamped it as tight as I could all winter long and then in the spring I removed the clamp and sealed the particle board with varnish.
It is still slightly swollen, but unless you know it is there you don't notice it at all. Never did replace the countertop.
Class C, 2004/5 Four Winds Dutchman Express 28A, Chevy chassis
2010 Subaru Impreza Sedan
Camped in 45 states, 7 Provinces and 1 Territory