ported vs. sealed boxes

I wanted to install a 15 inch sub in a ported box on my boat.  My installer advised me that with the sub I wanted, I would be better off with a sealed box and double the power that is sent to that sub.  He told me doubling the power going to that sub in a sealed box would give the same output compared to a ported box with half the power.  Also, by using the sealed box application the sub would not have to work as hard compared to the ported box.  He said with the ported box, the sub would be working much harder or near it max and the sub in the sealed box would not.  Since I will be boating in Arizona where temps hit 115 I thought that made sense.  Does anyone agree with this information.

I did read through the various configurations about sealed boxes, ported boxes on this site but I couldn't quite figure out if my sceanario fit.