Great idea to bring along the extension cord - sounds like you're prepared for just about anything!!
Well it hasn’t let me down so far! But if you want to do this, it‘s important to not get any old cheapo extension lead, because the UMC is not supposed to be used with an extension lead. I bought an industrial grade lead that has 10A plug/socket but is rated for 15A continuous draw, and a snib to lock the UMC plug to the socket. I’ve never had any overheating problems in the cable or socket.