Inner compartment dimensions are 70x20 mm. 

Now testing outdoors without any sealents as a part of 40 meter dipole antenna along with dogbone insulators: https://www.printables.com/model/310700-dogbone-insulator

Test update

Mechanical reliability is ok, casing capable to handle pretty intense thunderstorms with high wind speeds but there fogging issues. So if you plan to use it as a part permanent base antenna think about to fill it with gel compound. (Epoxy if you sure thats a final version of yours transformer) In my case i used thick silicone lubricant to fill any gaps between body part and cover and betwen connector and body