ah, another KCMO'er. Welcomez!
The answer to your question is not necessarily. I can tell you though, that IB setups are NOT ideal if you're wanting to go loud. However, paired with the right driver and a good install, they're hands down some of the best sounding setups I have ever heard.
As for box placement, it's heavily vehicle and install dependent.
Well, my situation here's interesting - I want a good loud car atm (relatively - obviously not going to set any records) - I'm on an extremely tight budget, I was going to get subwoofers, either some sundown e8's or some RD subs, but I have damage to my car from the last ice storm, slid into a curb off a hill, and my budget was just crushed from my quote for the repairs (My budget's gone downhill for months now -.-).
So, I'm looking at using some 6x9 speakers, that I was going to sell, but can't find anyone who will give me more than $30 out of them, and I feel I'd rather just keep them for that price. I have a hifonics amp, and I want to hook up the 6x9's into the trunk into a sealed box each, and low pass them @ 200hz or so, since they're primarily mid-bass woofers, and high pass my rear speakers @ 80hz. Giving me a nice good kick bass from the rear of my car. Definitely not good for a sound stage, but if I'm on a budget, I'm picking loud and not-so-good SQ over quiet and barely decent SQ.
In my old car, I had the 6x9's mounted IB style in my rear deck, but my mounting slots are too small, and I have some decent pioneer's mounted there too, so I wanted to see about getting more volume with a sealed box in the trunk for the two of them. I was thinking about attempting to mount them under the seats, still low passed, but I don't have the room.
I want no audiophiles commenting on all this -.-
And KC's a cool place. Nice to see several others from the area on here.
Also: Before I forget, it's an Infiniti G20, standard trunk vehicle, similar to the accord's/camry's/altima's you see.