I recently got the nice Hongdui KM17-Pro router plane and for a current project I needed a wider base so I designed a 3D-printed one.
It has 2 holes for M4 screws on the top and 2 spots for M4 nuts on the bottom. There is a 10.5mm hole at the top too in case you want to hang it somewhere in your shop.
Attached you can find the 3mf file that has the model name written on it and the raw stl file without the text.
You will need in addition to the print itself: