Mesh Viewer for Custom Inspectors // UI Extension

This tool allows you to render a 3D view of a mesh or prefab in your custom inspectors with multiple configurable options
These options include, but are not limited to:
-Preview window size
-Background colour
-Skybox
-Object position, rotation & scale
-Camera position & rotation (includes easy orbit method)

This tool is very easy to use and gives great results
The documentation can be found here