Here's wikipedia about the TT-30 connector. It's 120V at 30 amps.Confused. Are you saying the adapter I linked to wouldn't work with the juicebox? Or are you saying it'd be a waste of money and that it would be better to find a 5-15R to TT-30P adapter and use that with the EVSE that comes with the car to plug in if that's your only option? Just curious because I've come across the TT-30 receptacles a couple times and been unable to take advantage.
Also, I understand that the standard RV adapter for TT-30 to Nema 14-50 is wired differently than what the juicebox or other EVSE is expecting (because it's expecting two hots in different phases and that's not how the standard RV adapters are wired), but I'm curious why you say "you can't have an adapter" instead of "a better idea would be x".
The Bolt will only draw 12A if it sees 120V, so you're no better than plugging your stock EVSE into a regular household outlet (NEMA 5-15, 15A, 120V). Either way, you'll charge at 1.44 kW and get about 4 miles for each hour of charging.
If you just wanted to take just one EVSE with you and it has a NEMA 14-50 plug on it, an adapter would allow you to plug it in to a TT-30 and give you the same performance as the stock adapter in a household outlet. So it wouldn't necessarily be a waste of money. But you'd probably be better of bringing a NEMA 5-15 to NEMA 14-50 adapter though, since you'd get the same performance and probably see more 120V outlets you could plug into, since regular household outlets are much more common than TT-50 outlets.