I'm a big fan of Givi's Tanklock system, and have mounted it with great success on our F800GT and G650GS. But I wanted to post a small warning for anyone considering mounting it on their 390 Adventure.
In order to leave room for the fuel filler, they shifted the mounting plate back and angled it slightly towards the rider. The issue is, that puts it very close to the front of the seat.
If you mount even a medium-sized tank bag, the back of the bag moves into your seat area, and you will hit it unless you slide all the way back.
So I ordered the smallest Tanklock bag they have and it solves that problem, but you really can't go any bigger without moving the bag into the seat area.
If you're looking at the Tanklock system for your 390 Adventure, be aware that you might be limited to only their smallest tank bags.