Here's a link to some cool Photolistic panorama sceneries already made to work in FMS.
All you have to do is convert those images to .bmp files. and rename them to match what's in the .scn file
Copy and paste the .scn file , crash, and 3d files from a scenery that i made or some other skybox type scenery..
into a new folder and you're good to go. As long as the folder is not zip...FMS can read it from anywhere.
You don't need to extract the models/sceneries into FMS. Save it on a disc if you choose.

The sceneries are in SKYBOX fortmate already. It's the original aurthor of the many scenes that other sims use.
The work is complete and done correctly.

They are also in HD 2048x2048. Do the math and it's a 8192x4096.... 360x180 or equirectangular.
If you convert them to .bmp files, it'll give you 80-90 mb.

You can also change the uvxzy vaule of the skybox .scn file to give give it better graphics or resolutions..if you know
what you're doing.

http://www.szenerien.de/HELI-X-Szenerien/