Last in the current series, until I invest in anything new, and I've left the latest acquisition until last.
When I took the Honda to Denmark, I cobbled together a mounting system that did the job adequately well. I robbed the suction mount for the TomTom from the car, and mounted it to the top of the fairing under the screen with three self-tappers. The TomTom is a car unit and the mounting system is not robust, so I backed it up with a nylon strap glued to the back of the unit, such that if it vibrated off, the strap would catch it before it fell off entirely. This worked pretty well for a low-cost solution, helped by the fact that the unit was protected from above and in front by the Honda's generous screen. I had a ziploc bag in my tank bag in case of downpour.
Because there was very little wind pressure on the unit, this worked pretty well, considering it cost very little. But it wouldn't do for the Bonneville, which has no wind or weather protection at all, and no plastic bodywork to attach it to. A friend (you know who you are) came up with a surplus-to-requirements satnav holder. In fact, he came up with two: a rather smart Givi case, waterproof and well-made, and a cheaper device designed for use on bicycle handlebars. (He wouldn't accept any payment, so a donation to Help For Heroes was agreed as a quid pro quo.)
The Givi case was by far the better of the two (and at over twice the price, it should be). Beautifully-made, as I have found all Givi stuff to be, waterproof, and with lots of little extra pockets for phone and small change, it is a little jewel.
Unfortunately, it is also so 'universal' that it was hard to find a way to fit it securely to the Bonnie handlebars. There are yards of velcro straps and flaps, and by the time I had got a satisfactory fit, it was getting dark and time to unfasten it again. I may use this in the future, but probably for a longer trip where I can pay more attention to such things. For this trip, the other one seemed a better bet.
The Duragadget satnav case is a bit flimsy, as you might expect, as it is designed for bicycle use and "not tested above 20 mph", to quote one eBay seller. It isn't waterproof (with the zip closed you can see daylight through it), but it does come with a waterproof cover. This had become lost in transit, so I took along a heavy-duty ziploc bag from the kitchen, just in case.
It comes with a universal mount, and attaching it to the handlebars was a breeze. I chose to mount it on the left hand side, so it was easily visible but did not obscure the instruments. The attachment to the mount is only a plastic clip, but it worked well, and at speeds somewhat in excess of the stated 20 mph. I already had a cigarette-lighter type socket wired to the battery and stored behind a side-panel, so I plugged in the power cable to the TomTom through the little hole in the bottom of the case, ran the cable back underneath the tank bag, and plugged it into the socket which I had tucked into the map pocket. (It is a double socket, and I also had the iPhone plugged in there so I could use the MCN Ride Logger app.) Here it is on the bike:
(That's perspective - it's not really that big, as I keep telling them.)
All in all, it worked extremely well. The screen was reasonably easy to see, although glare was a bit of a problem at certain angles of the light. At times, all I could see was my hi-viz jacket shouting back at me. The ziploc bag I put over it filled with air from the wind and then flapped itself into tatters, so that part needs revisiting - probably curable with an elastic band round the bottom. Even so, the unit let in only a small amount of water, enough to dampen the case of the TomTom but not drown it. And it stayed in place at speeds up to x, where x is a number greater than 20, but less than 85. A bit.
OK, it's not going to be as satisfactory or permanent a solution as a proper RAM mount, but it performs the same function for a fraction of the price, and is perfectly adequate for occasional use. Price is under £20, such as this one on eBay.