John:
You may want to consider flanged 'inlets' for conncetions on the exterior for shore & gen. They are available with spring loaded flap covers.
A manual transfer switch @ 30/60 amps would be a better solution for selecting source, and would eliminate the 'hot' inlet.
Beefing up the cabling from the inlets to the xfr switch and to the panel to 30 amp (or larger) would also be suggested.
As to my comment re: Art 551, being the non-applicable article...you should/must still consider the other articles within the NEC for wiring methods (wire/cable/conduit sizes, etc).
