Project Winter

Ambushes are basically when you push one of the panels to open a bunker(any bunker not in the same tile of the cabin) Silver bunkers will only trigger ambushes not the brown shacks in the same tile of the cabin. You don't have to open then bunker to trigger just hit the buttons. It is RNG of course.

Legit method of getting this:

I don't really recommend going for this solo but if you must I suggest you are either a traitor or a hacker.
You can do this with other roles but you will be stuck out during events and possibly die.
Traitors can stay out longer and open traitor crates with food, firewood and other essentials to help with long periods outside.
Hackers have an ability to open bunkers with 1 electronic scrap if their ability is up.

If you are out and an event occurs or you are running from an animal and low on health, just go back inside the last bunker you opened or keep aware of your surroundings, usually going into a bunker or near certain objects animals can't get to.

Usually a few of the hatches South of the cabin will lead you to a bunker right next to it.

Boosting method:

Just have your whole group run around the map, including traitor so they can open crates for firewood and food, checking each tile for bunkers. It helps if you also have a ghost on your team checking as well and directing the group if they find a bunker.

With the boosting method you can easily get it within 10-15 minutes if the RNG is good even less.