Use your speaker to create a template, just flip it over and trace it closely onto a piece of cardboard or stiff stock paper. Now cut out the inside part, and tape it over the opening in your truck door. Using a template will allow you to move it around until the best angle and position is met (saving you from hacking the inside of you truck door to hell). You can probably use those metal cutting shears but that would be a lot of work, a dremel tool with a metal cutting blade would be an easily controlled method, or a cut off wheel with a thin blade if you have a steady hand and nerves of steel. Make sure you don't cut too much, or you will have nothing to attach your speaker to.

 

Great idea with the cardboard cut out.. Then I'll know just how much I need to cut.

Thanks much for the ideas fellas. Hopefully I can get these bastards in!

 

the snips were actually very easy, and i didnt have to worry about slipping and hitting a wire, the 6x9's are very close to the window regulator. I do work with sheetmetal on a daily basis so its probably more natural for me to use snips anyway