In the Electric Reach trucks we use an aircraft HO15 Freezer oil for the hydraulics (make sure you flush any reach, tilt or sideshift lines) and a synthetic 75W90 in the gearboxes. The manufacturer offers heater packages for the control handles and floor mats, in some high moisture applications you will need to look at water channeling for runoff in addition to your Dielectric grease for when the temperature increases to the freezing point or above.
In an extreme cold minus 40C blast freezer at one customer site we fabricated a plexiglass custom cab, installed a door on the reach truck and added a 3000 watt heater, (as long as you did not open the door you could work the freezer in your short sleved shirt) prior to adding the heated cab the workers were in 20 min out 40, they had shifts of three operators per forklift to get product picked and stored.