I mail ordered a Piaggio Vespa OEM chrome rear rack and an OEM Vespa top box from Easyparts and installed it. Here's how with pictures.

Note: this DIY is accurate for the 2012 (and later) Vespa LX 125/150ie 3V. The rack is now complete as opposed to the earlier design where the rack was an addon to the existing grabrail. The latest LX grabrails that ship with the scooter no longer have holes for bolts. The old design is presumably discontinued.

Some preliminaries:

1. Remove pet carrier
2. Remove battery cover (one Phillips type screw), disconnect battery leads (-+/+-), and put the battery aside
3. Remove fuel filler cap
4. Remove five torx screws that hold the grey plastic panel in place (one of the torx screws is bigger)
5. Fuse box must be lifted off
6. Gently push the panel away to the side; there is a cable attached with a zip tie -- leave them in place
Piaggio's cryptic Italian Montaggio instructions; page 1
Piaggio's cryptic Italian Montaggio instructions; page 1
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Page 2
Page 3
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Page 4
Page 4
Battery cover removed and the tools needed
Battery cover removed and the tools needed
The grey plastic panel is held with five torx screws
The grey plastic panel is held with five torx screws
Battery removed, fuse box detached and screws undone -- ready to go; wait, see the small screw in the lower right corner -- unscrew it and the plastic Vespa logo thingy comes off
Battery removed, fuse box detached and screws undone -- ready to go; wait, see the small screw in the lower right corner -- unscrew it and the plastic Vespa logo thingy comes off
Grey plastic panel stashed aside; it's a good idea to recap the filler tube to prevent screws from inadvertently dropping inside the fuel tank
Grey plastic panel stashed aside; it's a good idea to recap the filler tube to prevent screws from inadvertently dropping inside the fuel tank
Remove two bolts like this that hold the grabrail on either side
Remove two bolts like this that hold the grabrail on either side
These two bolts must come off in the rear; they are under the plastic Vespa logo that we just removed above; you will need a socket wrench to do this
These two bolts must come off in the rear; they are under the plastic Vespa logo that we just removed above; you will need a socket wrench to do this
So far we have removed so much; keep track of the screws, bolts and things
So far we have removed so much; keep track of the screws, bolts and things
A close-up look at parts removed, the screws and bolts and tools
A close-up look at parts removed, the screws and bolts and tools
The old grabrail had to go; the new rack replaces it
The old grabrail had to go; the new rack replaces it
The new top box is on
The new top box is on