Supportless;, in two or three parts, The arch act as a rail to guide the weapon and change the elevation to create variety.
The weapon needs no support to print but I would put some inside the rail chamber if I were you to secure it to the print board (fdm), just in case. The base can print supportless with a few defects under the piece, at the front base and the top part of the arch on near horizontal surfaces. add a few supports there if you don't like to sandpaper, or mirror the splitted one for clean full supportless (new).
Grab WeaponV2 ,added a few details on the weapon and fixed an unsupported surface inside the canon. Heavy ordnance (105x70x146mm).