We installed a ~36x90 tray in our 317RLOK. It does overhang the step on each side but small clear containers hold misc items and fit nicely on the step under the tray. We were thoughtful about where to place the tray based on putting our grill/blackstone/propane fireplace on 1 side and ladder/screen room on the other, so while it’s not centered in the opening it works for us. Being able to extend in either direction makes loading/unloading things much easier.
P.S.
Don’t judge - it’s a mess in there right now - we’re in the process of setting up/unloading.