design

Anyone interested in evaluating this diagram as I am second guessing a few things and just need to know if you see anything wrong. After thinking that I had this licked, I watched a video about battery efficiency, hung my head and went back to the drawing board. The specifics I am curious...

I have a 1998 Toyota Tacoma I would like to build a roof rack bed rack combo (kinda like a ladder rack) and after alot of googling I haven't seen it done this way often. Is there a reason other than center of gravity concerns that denies people from having a vehicle length roof rack of same...