I can not agree that a grid transformer, disconnected from the grid is vulnerable to solar storms.

The voltages induced by a solar storm, per yard, are very modest, and far below the normal operating voltage.
If however the transformer is connected to long conductors as would be the case whilst in use, then damaging voltages would be induced.

I would respectfully point out that a moderatly severe solar storm caused blackouts in Canada and the nothern parts of the USA some years ago.
Several transformers and other items connected to the grid suffered damage.
I am not aware of any electrical equipment being damaged whilst sitting on the shelf.

An EMP event produces greater electric fields, and can damage unprotected electronics, and might damage heavy electrical equipment.

Portable electronic equipment if totally enclosed in metal should survive all but the very worst EMP event.
Should certainly survive anything that the owner can survive.