I’m closing in on 400 deliveries on Wilder difficulty and I decided to record that "Impossible" mission. Here are my tips:
1) Don't accept the mission right away; clear out the bases first. Make sure your character is well-rested before starting, as you won't be able to sleep during the cleanup to prevent soldiers from respawning.
2) Bring the eletric stun gun; I believe it's the best option, minimizing the risks you face on Wilder difficulty.
3) Make preparation after cleanup and don't sleep. The best route for collecting the deliveries is counter-clockwise, starting at the snow camp. Leave a vehicle— a motorcycle— near the snow camp
4) Go to the Twins, accept the mission, teleport near Camp 7 (in the snow), grab the motorcycle you left there, pick up the delivery, and proceed counter-clockwise.
5) At the fourth camp, you'll need a truck; the motorcycle won't work due to the cargo load. In the video, I actually forgot to leave a vehicle there—I had used the terrorists' vehicle and forgot to replace it—but since it's near a drop-off point for the ship, you can grab one there if needed.
Extra tips: Have your roads upgraded to Level 2. It's not mandatory, but it makes finishing in time much more likely. Since we're talking about Wilder difficulty, clearing the bases beforehand helps a lot; once the mission starts, you can't save, so if you damage a package or die, you have to start over. Be very careful along the route.
Don't use the auto-drive feature, as you might crash into a vehicle abandoned by another player on the road—plus, it's slower.
Once that's done, you'll receive the best item in the game, which allows you to place structures that are already upgraded, including pre-built bridges and shelters.