I just downloaded the USACE charts for the Lower Mississippi
and intially had the same problem. Just a green outline of the area covered by the charts, and no detail. The charts did not show up on the chart list bar at the bottom of the OpenCPN window.
Then suddenly OpenCPN started to process the charts and generate the SENC. I can now display the detail on the charts and they show up on the chart list bar. I don't know why OpenCPN did not pick up the charts when I added the folder to the chart list, nor do I know what caused OpenCPN to finally process them.
Anyway, they do work in OpenCPN. If all else fails try forcing a complete rebuild
of the chart database.
Interestingly the charts do not display any depths.