Getting on the other end of the fiberglass bed

Hello.

I'm looking at doing a bit of work in the bed of my truck, and it will require me to actually get on the otherwise of the fiberglass layer of the , lengthwise of the bed.
(Or whatever material the stock bed is made of?)

By removing the compartments near the wheel wells, I can get a couple of places to either side, but I need to get more towards the front and back of the bed from there.

I need to be able to fit at least a wrench in behind there (a hand preferably too ), is there by chance that the rail (in the attached image) pops off, and provides all kinds of room for a hand and a bit of work?

From underneath I still don't have access to certain places I'll need to get to.

Perhaps other alternatives?

P.s. please ignore slightly elevated tonneau cover