Well I weigh more than 200lbs and I have crawled into the compartments to do some wiring
. The 2018.5 and up mid belly compartments ar not just the plastic bins, they have a metal frame and plywood in them so you should be fine. I would also try and tie into the vertical tube that is in between each door on the back side. The reason I choose to use the small door for my tool box build was because it was narrow and well supported... the wider the compartment, the more it will flex.