We just purchased a 2024 Leaf S, but unbeknownst to us, we are out of usable amperage on our 200A panel. Unfortunately, we have a lot of usage (hot tub, electric dryer, electric water heater, electric stove, well pump, etc.). Until we get rid of our hot tub (when it finally dies), we are planning to use a NEMA 14-30 dryer outlet with a splitter, like this one - https://www.amazon.com/gp/product/B0CD ... Z2T&psc=1 . This will allow us to charge at 24A without having to upgrade our panel and the service to our house to 300 amps or more. Unfortunately, our 14-30 dryer hookup is nearly 100 feet from where I'd like to locate the charger in our garage. Does anyone have experience running a 100 foot 14-30 extension cord from a splitter, through their basement, to a 24A charger? Other suggestions? Thanks.
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Use marine dock cord, it's meant for covering distances while carrying high current loads.

Is there a wire gauge or specification that should be used? Thanks again!

Shore power cords are monolithic and pretty much only come in 30A and higher. For 220V service a 50A 100-footer will probably be 6AWG, but you can go by rating and not really worry about the gauge. None of these manufacturers want to burn up anybody's very expensive yacht, so if it's advertised for a given amp rating, it will actually carry a lot more than that.