Pompeii stop-off visit while enroute Rome-Naples-Sorrento by train--practical or not?

That's an absolutely practical way to do it. This topic has been discussed on the Italy forum in the past so browsing through the previous replies will probably be helpful:

http://www.ricksteves.com/search?utf8=✓&query=Luggage+storage+Pompeii&search%5Bdestinations%5D=true&search%5Barticles%5D=true&search%5Bforum%5D=true&search%5Bvideos%5D=true&commit=Go%21

No worries with that plan, but certainly easier if you pack light for the whole trip (and keep your valuables secured).

Note that there's free baggage storage at the Porta Marina entrance to Pompeii, which is very close to the station. I used it once, and found it convenient and easy to use.

As much as I like Rick's books, I disdain the six-sights-in-a-day itinerary, and overnight trains to minimize down-time and hotel bills. But your particular need is exceptionally well-suited to the journey described, not a madhouse of activity. I would only comment that some visitors underestimate how big is Pompeii, and how much time it takes to see even a basic tour of Pompeii - especially without the help of a paid guide. It's also tiring amount of mileage, on hard Roman stone roads! Because we had no time limit, we walked all the way to the Villa of the Mysteries, which was important to me. I don't argue that it's a must-see for everyone. But the good news is that it's an easy 1/2 mile walk (on sidewalks, mostly) back to Pompeii's Porta Marina entrance, and the Pompeii Scavi train stop, from Villa Mysteri entrance.

In case that seems confusing, the name of the Circumvesuviana stop is Pompeii Scavi/Villa Dei Misteri. But the 99.9% most-used "entrance" to the ancient city of Pompeii is Porta Marina, about 500 feet from the Circumvesuviana. The Villa Dei Misteri entrance (no bag storage, not much traffic) is 1/2 mile away.

I'm with Tim. Don't underestimate the time it takes to visit Pompeii. Even if you are not a big history fan consider 2 hours to be the absolute minimum, better 3-4 hours. You can hire a paid guide at the entrance at quite affordable rates and they will give you a good 2 hour overview of the HUGE site before you continue exploring on your own.

That said, your plan looks very doable. Go for it!

Good point! Pompei is much, much larger than people expect it to be so you'll only cover a bit of it in a couple of hours. It's also likely to be very warm, and there's little shade so dress appropriately, and bring water. And use the restroom before heading off to explore!

Hey thx ! Great advice everyone. Esp re time to see it right.

Tom, personally I highly advise joining a good paid guide at the entry to the Pompeii ruins, and make sure you select one you can all understand easily. The guides know the ruins and the history well, can navigate easily, and know which areas may be temporarily closed for some reason. I tried to do the tour on my own with the RS book, and found myself often confused and somewhat lost, which then got me extra tired. As others have said, it's an expansive area, a whole ancient city. The street names in the book often did not match up with the street signs at the ruins, and of course no book can indicate what streets or individual sites might be closed off on a given day.