Storage of cast iron and similar tools

[Rhossydd]

it's so stiff as to be near unspreadable,

Could this be a case of having 'gone off' or having been a duff batch in the first place ? It's possible any solvents that made it easily spreadable have evaporated in storage (possibly before you first bought it).
Most similar products I've used have been of paste wax consistency, eg Kity speed.

What would be nice to use for hand tools in medium term storage is rust proofing paper. Companies like Veritas and Moore and Wright use it on their new tools.
The last item from Veritas I bought was wrapped in Uniwrap MPI which seem to be pretty good stuff. I haven't found a UK supplier, only available from Amazon in the USA (about £32 + shipping for a hundred yard roll). Too much for me to use in a lifetime I expect, but if anyone else wanted some it might be worth getting some via a personal import.

 

[Shrubby]

If you're covering the machines in plastic I would put bags of silica desiccant under the covering. Large bags are hung inside shipping containers and military equipment in long term storage
Some of the silica is self indicating - changes colour when saturated
Matt