First of all, welcome to Canreef. 
  
You could definetely do a chest or trunk to house your sump.  The only thing I can think of would be to make sure it's well vented.  You'll also need enough height to allow for a skimmer.  Also keep in mind there will be a lot of pipes for your plumbing that will be coming into and going out of your chest/trunk.  
  
I think if you could hide all that somehow it would be quite a neat designer type idea.  I like it. 
  
good luck 
		
	
		
		
		
		
		
	
		
		
	
	
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