Since you say you don't have a lot of experience with light painting, I'll guess you might not have a ton at night photography too - so here are some general tips to speed things up when you are out in the middle of nowhere.
The biggest time saver is to test things at your highest ISO first to work out your approximate exposure times -
For testing your ambient exposure out for light painting stuff - crank your ISO to your max ISO and use exposure math to figure it out.
(e.g. 1/15 sec at 12800 ISO = 8 sec at 100 ISO... or 1/8 sec = seconds, etc)
To meter it too, you can use your max ISO (12800, etc) and get a value there and then adjust it down to a >30second value - so if your meter says 5" at 12800, it'd be 10 sec at 6400, 20 sec at 3200, 40 sec at 1600, 80 sec at 800 and 160 sec at 400 - 320 sec at 200 and 640 sec at 100 - you can try a test shot at the 12800 setting to see roughly what the exposure of the ambient stuff (prior to doing any light painting) looks like - and then work back to your desired one.
(It sucks to do a 60+ second exposure only to find out that you only needed a 30 second one and the entire image is blown out)