[Antennas] question regarding dipole

[Joe Falcone]

Hello:  I want to run a dipole for 40 meters, 33 feet for each leg, under my second story deck.  I was  going to use insulated wire and staple the wire to the underside of 
the
supports of the deck. Purpose of the antenna is just to hook up to when I am on the deck to work some  100 watt CW.

I am going to fit the 66 feet of dipole into 40 feet by simply running the wire in a pattern like this  _|~~|__|~~|________ center __________|~~|__|~~|__   You get the
picture.  (I made the top lines wavy only because I did not know how to type them straight.  The wire  will run in straight lines). 

My question is:  Is there some type of rough rule of thumb on changing the lenght of the wire if you are  going to shorten the total lenght of the area that the dipole is going
to fit into, or doesn't it matter?  Would I still use the 33 feet?  This antenna will be up about 8 feet  from the ground, but the land slopes away from the house. 

Thanks, Joe. N8TI