Trying to develop a Skybox ???

Hey guys I have been working on this map off and on now for a while. I am trying to develop a proper skybox but I am not sure how to go about it. I don't want to make a huge box around my map its just bad. Also on a side not I'm not sure how I should place my hint brush'es in my outdoor area suggestion would be appriciated D:

RaVaGe, thanks for the hint suggestion that will help a TON!. I should have been more specific about the skybox I didn't mean a 3D one I know how to do that What I meant was how would you suggest I draw the actual skybox texture over the map instead of making one giant box around everything and hollowing it out bleh. The wire frame pics above show what that would look like and its horrible lol.

Well I am deffinetly trying RaVaGe's idea. Still thinking about the 2D aspect thanks for the idea though PoignardAzur.

I am thinking about shortening the map up to but its hard to find stuff I don't like after spending so much time on it. The I like the outdoor area and probably won't touch it. It has a tunnel system to I already shortened up quite significantly. The interior has some confined area's like short little hallways that connect rooms that I feel are kinda uneccesary.