I've pretty much run all around the area but it seems surrounded by mountains. How can I get there? It's the last place I need to give the new codes. There also seems to be way too many of those annoying bugs around!

Have you been to Jacobstown yet? The way there is around that mountainous region.

Follow the road.

Head straight from Silver Peak Mine.

I haven't discovered Jacobstown or Silver Peak Mine yet. I've discovered the Sasparilla factory near the outpost, and also Vault 22 (21?) just north of the outpost. But I can't seem to find my way into the outpost (or even see it), and as far as I can see, there's no road leading to it.

This one drove me mad at first too, like you I was trying to approach it from the wrong side of the mountains. Jacobstown's at the end of the road leading to the NW corner of the map. Follow that road and you'll be on the other side of the mountain range that's currently standing inbewtween you and the Ranger station. Essentially, you need to approach it from the west, not the east.

Thanks!