Thoughts on a “limited” portal mode?

Background: In a normal playthrough, I use portals liberally. Like putting a portal at every crypt, burial chamber, silver ore location, farming spot, etc. And I always carry portal mats with me so I even have a "portable" portal.

I recently started a no-portal run. While it was a bit too tedious overall, I really liked some of the changes the gameplay:

• I had to build roads.
• I had to build at least semi-permanent outposts.
• I had to raid via boat a lot more–like a real Viking!

So my question is: what rule changes would make for a good limited portal mode?

Idea #1 – You can't teleport *any* metal including nails, armor, weapons, and tools.

I really like this idea as portals only make sense if they link two safe locations, and are mainly only useful for supply runs. It would be a major annoyance, though, to "undress/dress" every time you teleported.

Idea #2 – Portals can only be built at ruined stone towers.

(Assume portals can only be built at certain "magical" locations, and long ago the precursors built a stone tower at each magical location). I also really like this idea. As a bonus, it makes the Plains more difficult since you can't have any portals there. The only downside I see is access to the Sacrificial Stones, but to be honest, I mainly use Eikthyr's power for the first part of the game and then Bonemass's thereafter.

Thoughts on idea #1 and #2. Any other suggestions?