1) Create the Image Texture maps your skyboxes images 
using one of these tutorials:

SkyBoxes With Bryce 5
Skyboxes with Terragen

Save textures at lest 512x512, recommend 1024x1024

2) Build your sky box in JDesigner3D
You can start with the 'new map' cube that is there when you
You start jDesigner by default. The sky box needs to be smaller.
This to optimize the draw face count. and framerate.

2b) Apply your skybox maps to the inside 
four walls and ceiling.  

(Above) The alignment to make these seamless textures
Of the skybox can be tedious until we get a function like 'Texture FIT'
to JDesigner3D

2c) (above) Set all 5 to "Full Bright"

2d) Next- (Below) Select the "Floor" of cube, and check "Invisible" 

3) Add PortalObject

3b) Place it in the SKYBOX you just made.

Name it 'Skybox', the editor increments the number onto the name 
so you don't need to postfix it as SKYBOX1. 
Say if you use more than one skybox.

3c) Position the Portal Camera. 

Note: the camera is "Sideways" and not pointing up from the bottom 
into the cube. This is the way SKYBOX's are done. It is not a bug.

4) Enclose your Landscape and  in a box cube.
When you build this 'Surrounding cube', Always make the top or ceiling as high 
as the highest point in your world.  So to not cut off a church steeple of 
mountain peak for example. 
Don't make it any higher than is needed, so to keep the world
'ceiling' slightly above the highest point.

(above) You should use a dark shaded Terrain or surface texture if you 
know the level will have a night sky. Shown is a flat terrain.

5) Select the four walls and ceiling Inside CUBE wrapping your outdoor level.

(Above) Use the settings shown, but in the portal. You need to set 
ALPHA to zero so you don't see the texture that used to be 
shown on the walls and

'Deselect all' to see the results better.
This provides a nice big SKY feel to the level though in this level the 
ceiling is actually only about 224 units high.
(about 7 feet) That is the special thing the SKYBOX property does when 
it is checked. It creates the illusion of huge distance.


Adjust the Portal Cam in the sky box for better "Tweaking" of the sky line.

You can adjust the Portal Camera position in the skybox in one of the views: 
TOP, SIDE or FRONT, while watching in the 3D view port in real-time.
Commonly done to get it set just right according to your estimated 
Players perspective view.

That about sums it all up...

-Ken Deel