Response from the OP:

1) Thanks much for replies to date.

2) Google search brings up numerous public parking garages in the
Inner Harbor area (a dozen or two within 3 or 4 blocks of Harborside).

Anyone know what their rates might be for a 24-hour overnight stay?
(Haven't found this info on the web yet.)

3) Does the Fallsway Park & Ride setup still exist?
(Wikipedia and other online sources describe it as having
existed in the early 1990s, then being cancelled)

If still alive, does it have one-shot transit connection
to Harborside/Sheraton Inner Harbor vicinity?

And does this function (both ways) into the evening?
Maybe until midnight? At reasonable intervals?

Thanks again.