Thank you folks for your replies. Your suggestions are awesome. Most of them I had not thought of.
Here is my list:
Bug Ross for more details.
Beat Bryan to digging the hole
Water lines and a sump drain with pump.
Removable portion of roof to service traction batteries. ( What do you guys think about building a shed over the buried room for service equipment. I do like the idea of having a hoist to lift and lower instead of relying on my tractor or forklift. )
I am thinking of cement floor and drainage tiles along with cement filled blocks as Ross has done with his walls. Cement or even treated lumber roof as Wolv suggested.
A of J, I will post a picture of my dig location when the sun is out tomorrow. The area is flat. When we do get rain, I get a steady stream of run-off over the planned site so I will have to build the location up around 6 inchs to keep from creating a storage tank.
Tom, I thank you for reminding me of the battery weight. I have one which my tractor does not like to move. 3000lbs.