Laminate floor only where you walk. Under the gaucho(s) or in the cabinets is unnecessary. It doesn't seem to matter whether you lay it across the long axis or with the long axis as the width of the planks spreads the weight. Laying on the long axis is a way to find out how irregular the floor plan can be with some interesting cuts necessary to fit to the cabinets, enclosures, etc.
As for frame rot, if water gets and stays under the floor, the frame will suffer. My Minuet had a trashed stove and furnace because of leaks through the vent pipe opening in the roof. The floor was perfect and the frame did not seem to be compromised as the aluminum did not hold the water.
1978 Argosy 6 Metre Minuet
2006 Toyota Tacoma