6.5 speakers how much air

putting 4 6.5 infinity's in the boat. running full range does air space matter?Old boat so making cans out of pvc for inside the boat.Next to the side,but it is only about 5 inches deep at the point where I was going to mount them.Should I cap the back of the can or will that be enough air space to run the speakers?Will be running at least 75 watts to each speaker.

I recently built some tower speakers out of stainless steel pipe, 6.5" diameter. I put in Polk speakers and according to their tech support, I needed a tube 13" long at that diameter to have the right air volume.

I did it recently with Infinity 625i's. I used 6" PVC ....11 in long. They look and sound great.

Air space isnt going to make a huge differance in full reange speakers, you will loose some power. Remember that most speakers in cars arent in sealed encloseures
I would use the pvc to mount the speakers but leave the back side open

No real difference. Sealed speakers sound better and you may get more low end in bigger chamber, but once you cross at 80 to 120, it will not matter.

Thanks guys thought about if I did not seal the back would water or crap get in the back.I doubt it because it will be a tight fit.The boat is an 86 nautique 2001 hence there is no places for a stereo or speakers,therefore making it up as I go....