Ok. 

File/export: wavefront object/ single frame. Click the universe box, all objects will then be deselected in the heirarchy. Click each box corresponding to each primitive that comprises your prop so that each has an x, you want only those objects with an x. Click ok. Make sure all options are unchecked except for 'include existing groups in polygon groups'. Click ok. Name your object and save to wherever is convenient.

Delete or hide your original objects. File/ Import: Wavefront Object, uncheck all options. Find your file, click Open. Your prop is now one object with 3 groups named according to their comprising primitives, accessible and editable via the grouping tool. It also has a single material per comprising group named preview:1, preview:2, etc.

Do you have wings3d?

---

W10 Pro, HP Envy X360 Laptop, Intel Core i7-10510U, NVIDIA GeForce MX250, Intel UHD, 16 GB DDR4-2400 SDRAM, 1 TB PCIe NVMe M.2 SSD

Mudbox 2022, Adobe PS CC, Poser Pro 11.3, Blender 2.9, Wings3D 2.2.5

My Freestuff and Gallery at ShareCG