Warning
This requires a newer version of Steam with Proton >4.2 support.
Importing models into the Source SDK under Linux requires a newer version of Steam with Proton and Forced Compatibilty mode.
Since the Source SDK is not supported under Linux, install the Windows version of Source Base Singleplayer 2013 using Proton in the Linux version of Steam.
Use the Windows tooling installed through Wine since the tooling in the multiplayer and Single Player SDKs are compatible. Tooling for modelling, mapping, particles and more will be installed when the single player base 2013 is installed. The assets are then exported to the Multiplayer version of LuminousForts. Under Windows the tooling is avaiable without having to install the single player sdk.