Modern Vespa

See pics. I think the engine cover has a couple small rivets at the ends to secure the rubbers. But I can t see any holes

No rivets on that one. It just get sandwiched between the cowl and frame. Put the seam towards the bottom so it's discreet.

If it's stubborn, I guess you could put some painters tape to hold it in place while you get everything threaded and in position. 🤷🏻‍♂️

Engine cover on the VNA does has one small rivet at the back holding it in place. Glovebox side doesn't. Or maybe that was just the Allstates? I dunno but all 3 Allstates that have come to me have had the rivet.

It's rubber... it's a DIY hole

Beig winter, if it's cold, just warm the rubber up in a pot full of hot water, then it will be softer & when fitted will "mold" to the curves better... just DO NOT cut the end off till it's cooled down, just in case it shrinks a bit... you don't want too much gap.
A bit of gap is good, as any water that gets into side panel can drain out