I went ahead and loaded several maps onto one 4gb card using Mapsource. Quite a few in fact. I chose BlueCharts from Americas 2008, HSA500L South America, plus land maps from OSM Caribbean and an Ecuador set. All seem to be displaying correctly when choosing to hide various sets in the Map setup screen. When on the water, I will activate BlueCharts and switch when on shore.

I will, however be taking individual map cards, just in case!!!