Haha, I was also caught in those construction areas for more than an hour a month ago on the way to Pozo Almonte. Chile customs asked me to take off my tailbag and put it through x-ray but nothing for my riding partner. I believe the aduana is for agricultural control between regions (Tarapacá and Antofagasta) or maybe just as a double check against Peruvian imports. South from Pozo Almonte, we actually found a gas station on the left side of the highway around Victoria which is I believe only 50km south of Pozo Almonte. We must've hit the gas station at the right time since we had no line. Hope you get to do the drive from San Pedro de Atacama to Purmamarca one day (high altitude pass, great scenery and animals and super twisty roads). It's probably my favourite of the trip.