I have a Generac/DeWalt generator that'll be plugged to the house via transfer switch, & I need an all weather enclosure to store & run it in. Any suggestions?

No complaints with my Rubbermaid storage shed - Keeps the generator dry, reduces the noise level by a few dB, and is big enough to also store a few fuel cans.

I would think ventilation is needed if you're going to run it from the enclosure.

This or a similar company or DIY
https://www.jamarcarports.com/carports/

Yes, definitely - I installed a pair of aluminum roof vents on the back side of mine, with a 10" AC muffin fan inside one of them. The fan plugs into the generator, and draws cool air in near the bottom of the shed - the other vent allows hot air to escape near the top.

I also installed foam gasketing around the door edges to help keep sound from leaking through them.

Coincidentally, I used it just last night when we lost utility power during a heavy rainstorm - Being able to keep the generator dry while it's running is nice.

Those are great ideas. Did you vertically align the vents on the same side as the generator's exhaust?

^ I have a "personal collection" of around a dozen portable generators (mostly under 2KW) - any one of which could be put in the shed when needed.

There is no commonality in where their cold and hot sides are - so I didn't make any particular effort to locate the vents to accommodate them.

Basic physics was the only consideration: Since hot air rises, at least one of the vents should be located high in the enclosure, so as to give the heat an opportunity to escape.