The OP asked about joining 10 and 12 gauge wire. With 12 volt RV wiring we often face even bigger challenges. I rewired a small NovaKool compressor refrigerator. The wiring run was pretty big so I needed 6 gauge. I just finished replacing my old Elixir charger/converter. I needed to work with 8 gauge wiring. I could not find any suitable connectors at my local Lowes or Home Depot so I ended up using gigantic wiring nuts which were marginal for joining single strand to multistrand.
I suppose now would be a good time to look on Amazon or elsewhere for better connectors. I could redo some of my past work and be ready for the next project or repair.
