I think Campingman has a good suggestion; Clean all the battery connections including ground connections. The fact that you drove 400 miles and couldn't start it really points to bad connections, especially if the 'alt' light or gauge didn't show a problem. Once you get everything cleaned up, then take voltage readings at the batteries. Start engine and get a second reading. Charging will of course be indicated by a higher voltage. Then shut down the engine and try readings again, this time on shore power. You'll soon discover if both chassis and house batteries are being charged or not.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI