I am leaving with my husband and 3 children in 2 1/2 weeks for a month in Italy and Switzerland. We have honed our itinerary and the last wrinkle is our trip from Venice to Naples in early September. We really want to take the night train so the kids can have that experience.
Do we need to bother with reserving couchettes before we leave, or can we do it when we get there?
This train doesn't usually get full, does it?
We have train passes, so I am not quite sure how to reserve online. Any help out there?

Overnight trains between northern and southern Italy can often be full in my experience - i was in Sicily recently and wanted to take a couchette to Milan and was told, in October, that all couchettes were sold out for two weeks. I could and did pay more for a place in a triple and if you want say a double and a triple it's easier to book right before the train - because they cost much more.
If you were to be in Italy some days before the train yes probably OK but don't just show up.
Go to www.trenitalia.com and book the night train online - you could even get a deeply discounted fare you would not get at the station.
The site is notoriously fickle it seems as per many complaints posted on Fodors - but the good news plenty of Fodorites will walk you thru it if you have problems. That's the way to go for sure.

Hi P,

>Do we need to bother with reserving couchettes before we leave, ...
We have train passes,..<

You should buy your couchette reservations as soon as you get to Italy.

Since you have passes, you can't make reservations online unless you go through an agency like Rail Europe or Euraide and this would be costly. As PalQ says, night trains often sell out.

I know it is possible for passholders to reserve trains in France by calling SNCF directly.

The wording on the information page on the Trenitalia site suggests that you can do the same for trains in Italy. Phone the Trenitalia Call Center. Dial your country's international access code + 39 (country code for Italy) + 89 20 21.

Thanks, all, for your help! We'll let you know how things go when we get back in October!