Since I don’t know a thing about your set-up, location, power level, etc. the following may not mean much but can work as a guideline.
You said “outside generator.” If it’s portable you can simply store it inside until you need it. EMP and lightning strikes won’t be a problem.
If your unit is wired into your dwelling electrical supply and built to automatically engage during a power loss this might be helpful.
Assuming your backup runs on a motor fuel it should be located away from the dwelling, not under an eave, nowhere near a window, and downwind so far as predictable.
There might be a powerpole nearby and that pole should be fit with a large copper wire top to bottom and coiled at the bottom of its base. That should be insurance from a lightning strike, which is part of the risk of damage. The unit should be six feet or more from the pole since lightning can jump sideways.
If there is no power pole a large nearby tree might be enough. In any case one needs a taller target to attract electrical surges.
If your unit has an engine then it can’t be enclosed in a full blown Faraday cage since it need air and room to exhaust.
The next best protection from a magnetic pulse will be a wire cage, covered as much as possible but not preventing access, and a few feet in all directions from the unit.
A fine pattern copper mesh would be best but hard to acquire so go with galvanized steel wire. Construct it with some rigidity and equidistant all around from the unit and it must be well grounded.
If the unit is not automatic then a portable, rigid cover, would work just fine. And remember that electrical pulses can come from numerous places. Solar flares come to mind. Even your own utiliy system can do damage. A recent truck wreck in my own neighborhood managed to cross a couple wires that sent a surge backward in our system. It did quite a bit of damage to folks that didn’t have built in surge protectors——which, by the way, is something else you should have in your normal power supply.
Hope this helps-——be prepared
Thank you for the info. It is big and wired in automatically. Think the size of two large trunks side by side. All encased and with a lid. Yes it has an engine and I wondered about the air factor. Runs on our LP. So the steel mesh is a good idea. Regards. MWH