I'm thinking now I'd like to keep the free supplied adapter cable in the car with me and get the HPWC for home, even though we just installed the 14-50 plug. I don't mind using the HPWC at 40 amps still so was hoping there was a way to just wire it with a plug into the 14-50 outlet instead of directly to circuit breaker, etc. Has anyone else did this? Is there a good/dependable plug/wire set available already? Sort of like you would do with other wall chargers that plug into a 14-50; like Chargepoint Home, etc. (EDIT) So after more research looks like you can just get a 2nd UMC and keep that with you as some people just mount those on the wall. Any links to solid/reliable mounting ideas out there - besides the coat hook solution?
You can just wire a lead to the HPWC (look for a 6 gauge electric range lead with a 14-50 plug). However, I don't think this is "legal" since the HPWC is designed to be hard wired. To make it legal, wire the HPWC to the box where your 14-50 plug is installed. If you want to use your UMC, you can buy the wire hanger separately from the Tesla store. It's only $25 and is quite attractive. Tesla Gear Shop Replacement Wall Connector Cable Organizer I'd recommend buying an HPWC which is $750. A replacement UMC is $650. You'll need to buy one or the other. You don't really want to leave home without a charging cable.
Designed for and required are two separate things. I looked for it once and did not find any requirement that it be hard-wired in the instructions (which would trigger the 110.3 manufacturer's instructions section). Provided that an appropriate listed receptacle is used (14-50) with the 50A setting along with appropriate cord, it is my opinion that it is not unsafe nor illegal to connect the HPWC via a stove cord on a NEMA 14-50 (it's permitted by art 625). HOWEVER, you're limited to a 12-inch length of cord per section 625.17(A)(3)(a). It may not be longer. I would go with the HPWC over a second UMC. It's built sturdier, the cord is longer. I don't have any instructions for it, but you'll need an appropriate cord clamp on the HPWC, a length of 6/3 SOOW rubber cord, and a NEMA 14-50P plug. Black and white will go to the outside two blades (hot) - wrap the end of the insulation on the white wire with electrical tape to remark it as a hot conductor. Green goes to the round ground pin, the center blade will go unused.
Thanks for the advice and ideas! To keep it easy, I just ordered a 2nd UMC to mount "creatively" in the garage with the cord hook. The more I think about it, just for a feeling for confidence I'll be able to charge almost anywhere, I want to have a UMC in the car all of the time - just in case, and if I don't, I'll forget it or it'll be a pain to pack up and unpack on regular basis. Thanks again!
Don't forget to buy the other Tesla adapters if you want be able to charge anywhere (10-30, 5-20). And consider buying the Chademo adapter if there are any in your expected long distance driving radius.