when making the 3d skybox a good idea is to duplicate the main level , place the sky camera at 000 in the duplicated main level , scale the duplicated main level down by .0625 then move the now 3d skybox to the side and remove all brushes and entities except for the ground your 3d skybox is done compile and test
#sky_camera issues
autumn harbor
autumn harbor
heres a test vmf i made , when you look inside the 3d sky box the dev ground is the size of the main level and the ground texture is what will be in the 3d skybox area , you can scale up the 3d skybox to see how it fits