What type of DC plug powers your Macbook? It may well be easier to power it from a small PSW inverter and live with the losses. At least it will be a straightforward installation.
Never had any issues in 4 years of full time travel.
Originally I used 3rd party DC plugs but I now just cut the DC leads about 150mm from the original power bricks and although they are not designed for high current use I fit an RCA plug/socket to the join maintaining mains operation when required. I am still on the original RCA plugs. Quality plugs and sockets are available from Jaycar.
They also stock other DC plug/socket combinations that may be more suitable for others.
I have run a 12V fused lead from the battery junction box to a dedicated wall plate at shin level in our living area with switched 3x 19V, 2x 5V USB, 2x 12V DC and 1x 12V cigarette lighter sockets. They are occasionally all in use.
Establish that the DC supply leads are a 2 wire setup before you cut if you decide to go that way. I have seen for example an HP notebook with a 3 wire lead apparently with a feedback loop of some kind.
A much easier option would be one of the many available 12V cigarette plug powered step up notebook power supplies if
you can find a suitable model with the right voltage, current and DC plug requirements. Or you could fit you own plug.