What sort of wood joint should I use for a hanging LCD Mount?

I am living in a dorm where I cannot drill holes in any of the walls or furniture. I have a wardrobe at the foot of my bed that I would like to mount my LCD monitor onto the side of. (to allow me to be completely lazy and use my computer from my bed.)
I have a standard articulating LCD mount, but because I cannot drill any holes into the actual wardrobe, I have decided to try and hang an L shaped wooden mount down from the top of the wardrobe that I can screw the mount into.
I will hopefully have a wooden piece running across the entire top of the wardrobe (about 4’ wide by 2’ deep) with a quite heavy (40 pound or so…) computer sitting on top of it. There will be a second board that will probably hang down a foot or two at a right angle from the piece of wood on the top of the wardrobe, and the mount will then be screwed onto the hanging board as per usual.
the monitor is a 24 inch that weighs about 14 pounds, and the mount extends to a maximum of 23 inches from the wall
First off, Is this likely to go badly?
I figure that leverage is on my side, as long as I have my 40 pound monster weighing the top board down, It would seem to me that even when the mount is extended to the maximum it will not be a problem. (perhaps I am wrong)
what I am really worried about is how I should go about making the joint in the two boards so that it will be as strong as possible and not drop my monitor.
I am rubbish at woodworking, so I really don’t know what the best way to approach this kind of problem would be. Is there some sort of relatively simple wood joint that will withstand the strain better than a simple butt joint. Should I use some of those metal L shaped shelf bracket things to reinforce the joint?
any help or opinions would be appreciated.