Protect my 6 by 9 from subwoofer air

I have 2 6 by 9 speakers on a rear deck and the bottom is exposed to the trunk where my subs are. WHen my subs are pounding the air pressure  from them is loving up my 6 by 9's so i wanted to buy a 6 by 9 wooden box enclosure and the guy at the store said if you put them in a box they will sound doodiety so he told me he could get me these plastic cups that go around the bottom of the speaker for 40 dollars and it wont effect the sound quality is this true or is he just trying to make me buy that. the duce

$40 is pricey. Check out crutchfield.com for speaker baffles. They have them by the pair for a quarter of the price.5.25" Components & 5x7 Coax Kappas w/Power Acoustik OV4-800

KAC 7252 powering 2 D3 8" Diamonds

KDC-MP728, KGC-4042A

Even pep boys sells those for less.

excuse the language but i live in canada and they are big c**k suckers here they hardly have any choices between brands their prices are high and they never have doodie in stock. Where can i get those cheap in toronto. :Dthe duce

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-790

http://www.crutchfield.com/S-VH5hSF96Ogw/cgi-bin/ProdView.asp?g=762&I=237XT69

My question is this: If he says putting them in a box will make them sound like "doodiety", how can he justify 40 dollars for baffles, which are really just "boxes". They both do the same thing! My advice from here, RUN from that installer, as far and as fast as you can, he's a shyster, and I say that with no reservation. Find a reputable installer in your area, there has to be something else...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."