1. Make an enemy.(optional)
This can be achieved relatively easily, by hitting a full kevlar repeatedly with a rock, or just spamming the mic and annoying him into shooting at you.
2. Follow him to his base.
Usually heavily armed characters do not move far from their base, as they are most likely near item/material spawns (Resource Valley, Resource Hole, Hangar etc). This means following them should, as previous be relatively easy.
3. Collect materials.
2-3 rocks and woodpiles worth of materials should be enough. Smelt the metal into fragments and the sulphur into, well sulphur.
Craft the secret weapon… A Handcannon! As well as one Handmade Shell if you miss. Use the rest of the wood to craft a foundation and dependant amount of pillars and stairs. Base this amount on how high the closest window or roof is. Remember only too craft 2 pillars per level.
Begin by placing the foundation onto the sides of his foundations. place pillars down on one side, so you use the building’s pillars to place stairs. Climb the stairs and jump through his window or onto his roof. If you are lucky, and your enemy forgot to put doors inside his house, you will have a free run to his sleeping bag. Destroy this. It will take about a minute. Be careful to not be heard, though that will be pretty hard in a smaller house. Once destroyed crouch-walk down into the storage room, and chances are the player will be crafting and or lookin into chests. From there it would be easy to kill him(handcannon is instakill headshot on kevlars), than steal his valuables and escape into the distance.