Who is your regional sales team and are you engaged with them on this project? Has any professional site survey/rf survey been done to model the layout of the shelves, show proper attenuation, etc?
In your drawing, which end will be the wall that has the APs mounted to it, the top or bottom? 300ft is doable with clear line of site so for these forklifts, are the antennas on the top of the forklift or are they integrated into the unit, and if they are integrated, where is the unit mounted inside the forklift? If the unit is mounted low, and has integrated antennas, then you will have the forklift+body+whatever else to get back to the AP at 300ft, which would be sketchy.
Do you have to mount on the wall or can you mount on the ceiling as well?