There are many Junction Box designs, but few which are round and surface mount like this model from NorthDesign. This is a simple  combination of the STL models into a 3MF profile with settings for quick printing.

It is 80mm round x 60mm height, with a screw on lid and four outlets with cable glands.  There are also seals for lid and glands.  It is recommended to print the case in PETG and the seals in TPU.

You could combine this box with other cable glands or grommets depending on your needs. Personally I find the collection of adapters from We Be Printin useful in connecting with 25mm pvc pipe for electrical conduit.