BigRiver did a nice chart of the Tesla adapters that have been offered but ironically NONE of those are an RV 30 AMP (called a TT-30R). On my 2018 MX, an RV 30 AMP (which is 120V) is only good for around 7 MPH charge rate which is not all that great. The max I can get from the Tesla mobile charger is around 21 MPH charge rate: that requires a 50 AMP 240V receptacle (a 14-50R or 6-50R). It just depends on how much you drive your X and how long you leave it plugged in each evening whether that 7-ish MPH charge rate will work for you.
As a new Tesla owner, it is handy to know about (and carry) a variety of the different adapters available. I've bought all the Tesla corded adapters shown above and quite a few other adapters from AC Works (so I'm never stranded due to not having the right plug). AC Works make a ton of adapters, pretty much anything you could imagine. I carry a bunch of adapters around in my frunk (both the Tesla corded adapters and some AC Works adapters that usually plug in to the Tesla 14-50 corded adapter). This is probably on the 'overboard' end of the spectrum, but was a small expense compared to the price of the X.
To use the full capability of that 30 AMP 120V receptacle, an inexpensive approach would use an adapter to convert from TT-30 to 14-50: that is the AC Works RVTT1450. Presuming your Model X comes with a mobile charger and a 14-50 Tesla adapter, you would plug the Tesla 14-50 into the AC Works 14-50R to TT-30P adapter, then plug that into your TT-30R receptacle. Then on the screen of your X, you would set the maximum charge amps to 24A (80% of 30A). You'd need to manually set the max amps to 24A because the Tesla 14-50 corded adapter sets the max amps to 32A (80% of 40A) and your car has no way to know you've installed that TT-30R adapter, so you have to 'help' your Tesla and manually set the maximum current from its default 32A (with the Tesla 14-50 corded adapter) to 24A.
Lots to learn at first. Fairly easy stuff though. Tons of different receptacles in the wild, all have different ways to adapt to them. And if you are ever adapting, you need to know that 80% rule: never charge at more than 80% of the rating of the plug (and breaker) you are using. When you are just using the Tesla corded adapters, they automatically figure out that 80% rule. But when you start adding other adapters, its just something you need to consider.