Persistent little beggars! They have moved from trying to create tunnels under the house to building them up the outside of the foundation. This is actually better/easier for me, since now all I have to do is rub the tunnels off once in a while, rather than do the long crawl under the house.

What I've done to date:

Destroyed all tunnels, dusted the sill plate and foundation wall with a heavy layer of diatomaceous earth. Poured a thick layer of sand around in the general area of the activity.

The last couple trips under the house showed diminished activity, though I did notice a new trail on the back wall, stem wall, which is now where they're exiting on the outside of the foundation.

Activity evidence inside the house is minimal, I think they're busy trying to recreate/maintain their tunnels to the ground. I'm checking the exterior daily, will do the under-house crawl in the next day or two.