Beautiful tank!!!  I can see why you would want something shorter to work on!!  Even with a background, the coraline will still grow and given how you maintain your tank, you will still end up scraping the back.  Definitely do not go with a tank that is 12 wide, you will end up with rock on the back wall and no room to move around!!   
  
I agree with Shelley, 48x18x18 would be a great size and you can't beat the height!! 
		
	
		
		
		
		
		
	
		
		
	
	
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