Get a 30-amp (or 50-amp) RV extension cord – nothing else

Yes, and you need either a 30-amp or 50-amp cord designed for RVs, not a household extension cord.

Most travel trailers and smaller RVs use a 30-amp cord with a TT-30P plug (the three-prong round one). Larger motorhomes and some fifth wheels use a 50-amp cord with a NEMA 14-50P plug (four prongs, looks like a dryer plug). Those are the two standard ampacities. Never use a standard 15- or 20-amp extension cord – the wire gauge is too thin, you’ll get voltage drop, and you risk melting the plug or starting a fire.

The cords themselves are heavy-duty: typically 10-gauge for 30