I make a lot of good use of my oscillating saw. Works well in tight places, and has cutting saws, abrasive cutting tools, and sanding attachments. Handy, and would make short work of cutting out the electrical panel.
Let me throw this out there for those that don’t need much electrical. I don’t plan on having anything mounted in my galley wall. I want that entire space for storage. I plan to mount my battery, fuse block, and ground bus to my trailer frame. and have my switch/outlet panel in a pod under my shelf. my wiring will come through the floor in front of the bulkhead at the edge of the floor and be tucked behind the headliner.