I had a few pretty serendipitous opportunities to get some thick Crepe Myrtle cuttings. I barely caught someone on my local Facebook pages that had trimmed several large multi-stemmed Crepe Myrtles and I was able to stop by and rummage through the pile before it got hauled off.
You can see below that after only a week or two several of the hardwood cuttings have sprouted leaves.
This is what I use to root my cuttings. This is a 2 ft. x 10 ft. x 1 ft. box filled with silica sand from Home Depot. I used two misting systems from Lowe's meant for the patio. I also put a timer that goes off every hour for 3 minutes. Then topped it off with a thick clear plastic sheet. This is in full shade all day long.
Here are the cuttings a few days later. You can see that the leaves have sprouted and have grown several pairs of leaves. Only one has roots so far and I've moved it and put it in a terra cotta pot mixed with bonsai soil and sand and put it back in the box.
This is a fantastic way to create material to be able to work with as Crepe Myrtles grow really fast and can be multiplied with ease.