Thanks to the link to the other thread, had never seen that before.
I was considering what type of soils might be best, but haven't had much chance to ponder. I guess I didn't pay all that close of attention to the soil, but there didn't seem to be much clay up where they were. Wasn't sandy either, but like dark loamy in most places. Then again, most of the forest floor was covered in litter, logs, misc. debris. Lots of the places had a very deep duff layer. Although I did not see a single larval burrow anyplace, I also wasn't looking that close. But certainly a fairly solid soil that holds together well seems appropriate.
I did collect many bags of native substrate - mixed dirt with duff and debris. Hoping a mix of this with some coco fiber is ok. I can tell you they are certainly copulating often and everywhere, so if the soil is remotely close maybe I will just get lucky?