If you hold all the cables in a bundle that you want to go thru one hole, how big of a hole do you need? (Allowing for a couple extra duplex wires).
A #1 cable isn't that big, other wires smaller.
Anyway, fit a commensurate sized piece of heavy wall hose, like stuffing box hose or heavy exhaust
hose thru the drilled/cut hole in the bulkhead, careful work
will obtain a hole that you have to kind of "twist" the hose thru.
Feed thru the wires/cables and squirt the hose full of foam.
You only need a few inches of hose.
Alternately: Are there means to support/fasten the hose on either side of the bulkhead?
If so, job may be made easier.