bondo's reply is remarkably similar to where we're at now. I started calling people and ended up setting an appointment with a small outfit from a small town near us that specializes in animal control.
The young man who showed up said our concrete block skirting was installed very nicely, and the overlapping Hardi-Board was very tight to the blocks. The problem is these split blocks are coarse. You can be in contact with the Hardi-Board at one spot, then slide your fingers along and find a 1/2" gap. We discussed drastic measures like removing all the Hardi-Board and installing a wide sheet of HW cloth, but he said the Hardi-Board would break and it'd end up being a big job. He thought he could get good results by simply bending strips of HW cloth into a "V" shape and stuffing it behind the Hardi-Board.
He said that they would also shoot expanding foam into the bigger gaps. I've used foam before. Mice blow right thru it. But he explained that if you shove the HW cloth into the gap first, then apply the foam, the foam expands into the mesh and sets up, creating a barrier that's tougher than just the HW cloth.
So we signed on the dotted line. Problem is, they never used any foam. I asked about it as they were wrapping up and he said the HW cloth fit so snugly that he didn't think they needed it. I'm annoyed that he talked about foaming before we signed, then didn't do it, but I can go around the perimeter with a coupla cans of foam.
We have two openings in the block skirting that allow access under the mobile, with screened wood frames blocking the openings. The animal control guys put heavier HW cloth on both of the frames. I cut up some metal flashing and attached it so that the flashing overlaps the gaps around the frames. The openings are directly underneath two doors on one side of the mobile. They're hidden behind some wood steps. When we first pulled back the wood steps, we found a handsome Northwestern salamander tucked into one of the corners. I scooped it up and released it in between some big rocks along a retaining wall we built a few years ago. My wife and I don't want mice under the house, but we think salamanders are cool
I was worried that the HW cloth would push the Hardi-Board away from the concrete block, but I don't see evidence of that, even at the corners of the house where it would be most evident.
It's too soon to say whether the HW cloth is stopping, or at the very least has drastically slowed down, the rodent traffic. And, as mentioned above, mice are persistent. So I don't think we've necessarily solved the problem once and for all, but at least we've done something
about it. Well, paid to have something done about it...