As Peter says, the motorbike ones should meet all your needs...after all the M3W really is a 3 wheeled motorbike
The only problem is that they are not cheap and it may be more cost effective to buy a cheap car one which can be replaced if damaged by wet. My brother-in-law laughs at my Garmin Zumo motorbike satnav and uses a cheap car TomTom one clamped inside the screen of his GS and over the past 4 years its shrugged off rain etc. RAM mounts should have something that you can mount the actual unit to the car.
I would definity look to having a bike satnavs.
Another advantage of the bike satnavs is they have larger buttons.
I have used my GPS (Google maps) on my HTC smartphone - and it is pants. Whilst driving the Morgan (e.g. nothing above to stop the signal) it will drop out. Dreadfull functioniality. too small to read with ease, buttons very small, touch screen impossible on the move - I can go on and on.
