If the differential rises above 20% between indoor RH and humidity level of the floor, that's when damage starts to occur.
I find that doubtful.
I'm with you on the effects of humidity swings like storing a trailer in very humid conditions and possible damage. A lot of these products have a chip fiber core and there is little quality control with some products (who knows what they are using for binders and glue?). Dupont, AFAIK, is the only mfg of laminate flooring that uses a synthetic core. Pergo makes a good encapsulated product. What you get with that is a HPL coating that is built better than your countertop. I also wouldn't be afraid of installing a name brand wood plank in an RV. If it's installed correctly and there isn't any standing/dripping water, there shouldn't be a worry. It's been done.