Ok found the issue; under entities.lua you have...
if mods["SchallTankPlatoon"] then
dar.equipment_grid = "tank-SH-equipment-grid"
elseif mods["bobvehicleequipment"] then
dar.equipment_grid = "bob-tank-2"
else
dar.equipment_grid = "large-equipment-grid"
end
The size of the Super Heavy Tank equipment grid is 6x5 so the equipment is enabled as available, however the grid is reduced from 10x10 to 6x5. Of course its possble in Schall Tank Platoon to change the base size of the tank grid though the options menu, but it might be better to keep the original grid settings and instead set the grid parameters to cover all the equipment...
equipment_categories = {"armor", "vehicle", "armoured-vehicle", "tank", "tank-M", "tank-H", "tank-SH"}
I don't know exactly how to do this though. I'm sure its easy enough.