RotoBelo!

After a fair bit of playing around I've decided that the Mango approach of a bicycle bell and a bit of string is the least awful way to get a bell into the rotovelo.
I had a pingping bell mounted next to the cockpit so I could reach out and ping it, but it was about 15cm from my ear which was not ideal. I've been looking around for a bicycle bell that I can bolt on to the shell and bike shops don't have many of those. The pingping bell mounts using an O ring so I just twisted that under a washer, which kind of worked. And on bike to work day I got a free bell with a standard clamp and one problem - the clamp is designed for a handlebar no more than 20mm in diameter, when normal handlebars are 22mm (this is why they were free). I grabbed one just in case, since they're no use to anyone else and I might be able to use it.
The other day I had a brainwave - a doorbell is designed to do exactly what I want. The actuator goes on one side of a barrier, and the ringing noise comes out the other side. All I need is a lightweight, weatherproof doorbell. So I had a look around and most of the ones I saw are designed for a thick door, not a 3mm velomobile shell. They also tend to be heavy (because who cares on a door). I did find one that I thought might work, but it was $30 and heavy, so I put that idea on hold.

Then David Hembrow's post on bicycle bells reminded me of the string idea and I decided to revisit it. The original problem was that my preferred ding-dong bells have short push arms and require a lot of force, which means having to pull hard on the string and also mount the bell very solidly. Not easy on a thin plastic velomobile skin.  But my free bell has a long press arm (perhaps 40mm) and a quick test showed that it's not too hard to ring it using a string. So I drilled out the rivets that held the mounting bracket in place and started looking for places to attach it to the RotoVelo.  Not an easy task, as the bits that don't get scraped regularly when I run up ramps are very visible. I ended up mounting it just in front of the cross member - closer to my head than I really wanted, but at least it's shielded by the shell from direct sight. I'd definitely more audible than the pingping bell and much quieter for me. Quite bearable, even with the cover off.
 (a couple more photos)
Plus I washed it. It seems odd to own a bike that needs to be washed.