On the sides of the light there are two tabs to get half of it off to replace the bulb. The rest just slides out after you depress the holding tab you should be able to remove the red part.
The base I believe is screwed into the bottom.
I am not sure though, but on my car it is like this, but I have not attempted to remove the base of it.
I did have a friend who just drilled a hole big enough to get some tin snips in it, then he cut out the hole for my sub port in a few seconds by hand. Was pretty simple and I came up with this elaborate scheme to use what I had to make my port extend into the cabin, which was done with some cardboard tubing, and all. To get it out is another story.
hehehe its fairly permanent without some dismantling.
Alon