While stacking fire wood, I was looking at my dump box. There are screws along the bottom and at the front of the side panel that hold the side panel in place, but there is also the top plates (#11 in the diagram) that have to come off. There may be some side plate screws hiding under those. (See Note below) Not sure if there are any side panel screws under the fender lip extension, it doesn't really appear to be so, but hard to tell from the diagram and they aren't visible on mine. Hopefully, if you can find and remove the side plate screws, including any under the steel top plate, maybe you can pull the side panel away enough to access the latch bolts.
Note: In the diagram, #3 are those annoying thread clips that the screws go into. My experience with those on other machines is they tend to fall off when the screws are removed and drop out of site or into a crevice that is inaccessible. So beware of those. Again, maybe just removing the rear and bottom screws for the side panel will let you get behind it to the latch bolts. What a nightmare design!