At the manufacturer level I've worked with 6 different smelters throughout Europe and the Middle East and there is no single solution that suits all products and locations.

Emirates Aluminium have never really used their Hyundai forklifts and as soon as they were on site they were parked up due to issues and replaced with Cat Lift Trucks.

If you want to protect cylinders then I'd say the easiest solution for future orders is order a different mast if possible that will keep the piston rods well clear of splashback. If I'm honest though this has never been an issue I've encountered.

10mm lexan is a bit excessive bearing in mind that it will need frequent replacement. Molten aluminium would not penetrate lexan half that thickness once it leaves the furnace.

Chains have no issues as long as they are lubricated frequently and for hoses you can get a fire resistant sheathing that can be slipped over the hoses to protect them. If Hyundai approve of the use of non-flammable hydraulic oils with their hydraulic systems then I'd suggest using it, because I have only seen two total loss forklifts both from ruptured hydraulic lines.

Dust filtration, magnetic fields and operation have been the biggest items Ive had to deal with and solve....with the magnetic fields being the biggest pain as its impossible to test until you are in the application.

Crownd, I know this is an old topic, but thought I'd chime in on the DP50K's you had issues with the drive shafts breaking in case you never got to the bottom of it. I found that the cast houses were using the side of the forks to push out hooks from the molds and to do this they needed to blip the throttle (bulldoze) spinning one tyre, which would then get traction and suddenly stop it's spinning i.e. massive torsional loading through the drive shaft.
On the 4-ton models with the one speed transmission it is unlikely you'd see the same drive shaft failures, because the gearing provides less low down torque in order to keep a similar top speed as the 5-ton units. In addition on the 4-ton as a factory option the 5-ton front axle could be fitted, providing beefier drive shafts and wider/thicker brake shoes....ideal for smelters.
For the 5-ton models a drive shaft with a thicker case hardening was/is available, which obviously does not fix the abuse part, but does make it a little harder to snap a shaft.
I had never seen drive shaft failures on 4-ton models in identical applications and only once the customer decided to use 5-ton models at a new location did they occur.