Where did you mount the PDM? There is not a lot of choices.I use a Garmin Drivesmart 71 as GPS. Does not rain very often here in Phoenix, so rain shouldn't be an issue.
Mount is a RAM Grip with modified 'Rubbers'.
I've also created a mount for the RAM Mounts which I put onto the Handlebar Holder (can post pictures).
3D printed, but even it would fall off / break, no impact to the handlebar etc.
Have also my phone mounted via Rokmount and added two power sockets (one with USB-C and USB, the other one for plugs with cigarette lighter plug (reason is the garmin, couldn't find any cable which does not make the garmin going into USB Connection Mode, but had to do something 3D printed as well)).
Amplink: I have the previous one, the PDM60 ... was a good choice. Would also go for the AMPlink now, but I don't see much advantage in upgrading, besides the waaaaaaant
I am thinking about making a bracket so I can get in the space between the mud guard and rear fender.