I found that if you start with the camper on its side, the flat will be vertical. Insert the bottom end in a position near the bulkhead slot, then one hand inside and the other hand in the outside top, you pull with the inside and push outside top and the flat will bow enough to slip into near place and can easily be moved to its final position.
Put your long wires through the holes in the hull and bend the wires down flat against the inside so they won’t fall out or interfere . When the galley flat is near position, thread the wires through the flat and twist. Long wires allow you to twist the ends so you won’t loose them and allow movement of the galley flat to slot it into the bulkhead and position on the hatch lip. When you are happy, tighten up the wires.