[BB_TX]

Looking at your floor plan and inside pics, it looks like the only option is to remove one or more of those panels in that cabinet. Or, if there is enough slack in water and propane lines and wiring to pull the water heater out to access them from the outside.

A little creative work could make those panels reinstallable adding some reinforcement on the back of those panels and using small indiscreet black screws from the outside without showing too much.