I don't think you will be able to park that rig anywhere in the Inner Harbor, so I would suggest parking outside of town and driving in with the Hummer.
We were barely able to squeeze our 40' coach with no toad into the one and only lot in the inner harbor that allows it (see here: http://ourodyssey.blogspot.com/2011/10/waterfront-property-in-baltimore.html
). I don't think you could maneuver a 45' coach past the ticket machine and into the lot, and for sure you'd need to unhook the toad (and pay for it separately) first. If you are able to get into that lot, it's across the harbor from the aquarium, so it would also be a bit of a hike.
Our backup plan was to park in the oversize section of the long-term lot at BWI and take transit to the Inner Harbor, which might also be an option for you.