So here is how I built my custom Movie Mylar Sign Lighting Box. I hope it is helpful for anyone out there that wants to make there own.
All my lighting product from ElementalLED.com
Light Bar (Neutral White 20"}
Light Bar Extension Cable (12")
Light Bar Conncetor to DC Plug-In Cable (Female)
DC Extension Cable
DC On/Off Switch
12V DC Power Supply (12 Watt)
Pack of Grommets
Tube of Krazy Glue
Get your custom box made. My dimensions I provided to a sheet metal shop and they modified it a bit because of bends and what not. My dimensions are 5" x 25" with a depth of 5". You can ask them to drill a whole for your grommit but I did that myself. Also make sure you have little lips on the inside of the front to hold your sign backer and sign. The pictures provided should help a lot too.
Paint your box the color of your choice!! I did mine black (I think that would be the more common choice).
Take your light bar and attach the clips to it. Line it up in your box on the back and make marks with a sharpie where the clips will be. Take down the bar using krazy glue around the edges. After the bar is on firm carefully take the bar off (Avoid pulling off the clips by holding the clips base down against the surface as you pull the bar out). Once the bar is off go crazy with krazy.. glue. Make sure that those clips will never come off.
Now that your bar is all done you will need to get your power source done. Insert your grommit into the drilled out hole. Test that your DC connector piece is nice and tight when inserted (This is why I recommend drilling the hole yourself, so that you can slowly make it bigger as need by using the drill on the outsides of the drill hole. You can do this by applying pressure to the sides of the hole while moving the drill up and down, Do a little at a time.. you dont want to make it too big). Once you have confirmed that the DC connector fits nice and snug, take the connector back out and put krazy glue around its outer surface so it will stick to the grommit. After it dries apply more krazy glue and some additional hot glue so this piece never comes loose from being plug in and out a lot.
Use the extension cable to plug in the power cable to the bar. You can do without this piece but I wanted to eliminate any tension on the wires.
Add your plexiglass backing for the sign. I used "Sign Lighting White Acrylic" from Tap Plastic . Make sure it fits well. If it does, take the sign back out and add krazy glue to the lips that hold the sign and re insert the backing.
So now your box is done. Use a 12V plug in adapter to power it. You can also use a lot of accesories on the LED website. I am using an on/off switch for now, but later I may get there 12v wall dimmer switch so I can hard wire my box and put it above the entrance to the theater room. Then it will have a easy and sleek switch to use. Hope everyone likes the box and finds this usefull to put one of your own light box's together!! =D