Any options for car adapters and magsafe 2?

I picked up a GoalZero Sherpa battery pack and solar panels last year when I was using a Dell. It turned out that it needed a secondary adapter for that, and wouldn't charge the laptop, but it would power it and keep the laptop's battery from draining.

Now that I've moved to a Macbook Pro (late 2015) that's no longer an option. There is a power inverter so I could just plug in the regular adapter, but the power draw is so high and it gets so hot that sometimes it overheats. It also loses a lot of power in the conversion, so even though the batteries are roughly equivalent in capacity, I only get around a 30% charge on the laptop.

That's not really worth it for me, especially since I'm going to be bike touring and might only get a single charge from the panels on a day. With the extra 7lbs for the whole kit, that's way too much weight for the amount of power I can use.

These are the ports on the battery pack:

• USB port (output): 5V, up to 2.1A (10W max), regulated
• 6mm port (output, 6mm, green, hexagon): 12V, up to 10A (120W max), regulated
• laptop port (output, 7.4mm, orange, square): 19V, up to 6A (120W max), regulated

The 6mm port has a second attachment that changes it into a car adapter style port. So that's potentially another option. Though I've read that there are some problems with the ones that do it directly, so it would be a _different_ inverter that I think would end up having the same type of power drain issues.

Thanks for any pointers on how to get things working!