jwelectric, you mentioned:
you could sit the panel on the ground if you so desired
But earlier you pointed out to 110.26(A)(1)(2)&(3) and noted:
Just to clarify, can the subpanel be mounted 4 feet above the ground? How about the headroom of 6 1/2' you mentioned.
It would be mounted on your suggested 3/4" ply board, making in the same high of my I eyes when sitting on the floor
Look closely at 110.26 and you will see that the working space, or the space in which one would be standing while working in the panel is required to be 30 inches wide, 36 inches deep and 78 inches high. This working space is the area in which one will be standing while working in the panel.
The panel itself can be mounted anywhere between zero inches and 79 inches to the center of the grip of the highest breaker.
In a dwelling unit I have never in 47 years pulled out a ruler to measure the panel. I mount the panel at a good working height for me.
If your heart desires to mount the panel so you can sit on a nail keg to work in the panel that is your choice. You can mount it as high as your heart desires as long as the highest breaker in the panel is no higher than 6’ 7” above finish grade.
You said you have 6 feet of head room under the house so you will need to dig a hole that is at least 30 inches by 36 inches so you can achieve a head room of 6.5 feet. Mount the panel at any height your heart desires as long as it is no higher than the bottom of the floor joist.
If your heart desires to install hooks so you can hang by your feet to work on this panel then by all means sit it on the ground although in my personal opinion this would be a lot of work for nothing and then you might have a family of Armadillos trying to bite your nose while you are working on that panel.
By the way have you ever had armadillo stew? Does it really taste just like chicken?