I would go with foam, if you don't have the spider thingeys, which are really meant to keep the wires from banging around
and are not really stiff enough to suspend the junction box unless you used 2-3 at each end of the box in an X configuration.
Other tandem builders have noticed the same problem. Most likely there will be enough cable slack to allow the box to be
accessed without unplugging the cables, but without disassembly it is hard to know where the slack is. You may have
more than one junction box, as the longest cable is 1.9M.