Have a Teltonika RUT950 or Teltonika RUT955 and regret not buying the surface mount kit at the same time? Plus, paying shipping costs for a $10 plastic mount is ridiculous?
Good thing you have a 3D printer. Because I've already solved that problem for you.
Clips onto RUT950/RUT955 side "rails". You can attach two of these to a single router if you want even more reliability. But a single clip should be reliable enough for most situations.
Holes were designed for 3mm screws. (That's the small screws you tend to get with IKEA furniture) FreeCAD file included if you want to resize the holes for your particular screws.
Supports should not be needed for a regular PLA print as long as your overhang performance is half decent. Different filament that's not as good at overhang might need supports.
Simply snap onto the back or front of a RUT950 or RUT955. Should snap in place and handle a fair bit of shaking without issue.
For extra strength/redundancy, you can attach two of these mounts and use four screws. Might be a good idea if you plan to mount it very high up, or in containers where it might get moved around.