I tried to find answers in the forum but was quite unsuccessful.

I acquired two boxes of unmarked IR film in a lot. (I guess it is Arista/Efke). I have shot IR film before just not ever 4x5.

Are the usual plastic holders suitable at all?
Does one need metal holders to prevent fogging?

If plastic holders are OK, how do you handle them on a sunny day in the field?
Special sleeves?
Insert folder only under the dark cloth?
Or am I overthinking all of this?

Any pointers from experienced IR shooters are highly appreciated.