The Multiplus II is the newest of the 3000VA inverter/chargers from Victron.
They are thinner and taller than the MultiPlus which makes them harder to use in a vertical mounting configuration. Good news, they can be mounted horizontally.
Mounting a Victron Multiplus II
From Justin Cook:
"The Multiplus II CANNOT be mounted on the ceiling. It can be mounted on a vertical wall either in a vertical or horizontal orientation.
DO NOT mount to the ceiling. Horizontally on a vertical wall is fine though, or upright, or flat on its back on the floor!
The MP-II utilizes a single toroidal transformer mounted to the rear of the case (as opposed to the regular MultiPlus, which uses two toroidal transformers, one on each side of the case) so while it shouldn't be mounted to the ceiling since then the transformer would be hanging by its mounts and fighting gravity (and I find that gravity always eventually wins), horizontal mounting has no effect at all on the mechanical integrity of the transformer or its mounts."
More on this subject.
Either the Victron Multiplus or the new Victron Multiplus II can be mounted on the bay ceiling in a frame hanging from the ceiling of the bay with the front face of the inverter up. Allow cooling clearance. The Multiplus II is thinner and longer, maybe a good choice for a mounting in a ceiling frame if clearance is an issue.