Now Jasum, what I did was put 3/4" screws into the left and right sides from the outside inwards (at a convenient height) and put the shelf back in on top of the poked in screws. Now it is a removable shelf. I take it out to water and what not.
I know you might catch yourself on a pointy screw inside the compartment, but I have yet to, and I do lots of things in there.
It seemed to be the easiest way (I suppose a bolt and nut would work too), but an angle bracket, or something like that, would let the bottom flange of the shelf slide between the wall and the bracket, pinch it there and be harder to get out after.
I also siliconed the holes incase gasses came out. Probably not, but I was bored.
2016 North Point 341RLTS
520watts of solar. Morningstar MPPT
4 6volt 235ah Surrette batteries
2017 F-350 Platinum CC SRW