I like to work with ported designs, and use them exclusively in my home sound system for all the woofers. The sub in my car is sealed, but on my next one (if this one ever wears out!) I might work on a vented design for that, too.
IMO, you can't use the manufacturer's data exclusively to build a ported box. Some of them give some very detailed choices to choose from, and give you tested responses with each of them...which is great. But most are very vague in the details and so you're left with some simple measurements to follow. You have to ask yourself, "Who are they appealing to with this design? Is it designed for high Q, more SPL, a noticeable peak in the response, to appeal to the majority of buyers who want more bass?
I will first look at a woofer's parameters to tell if it should be ported. Look at Fs and Qes, and do the division Fs / Qes. This gives you the EBP. If the number falls in the range of 50 or lower, use the driver in a sealed box. If it is a higher number in the 70's or above, use it in a vented. For that gray area in between, work it up both ways in a box-building program, then use your own discretion on how to build it. Personally, I will go with ported for any EBP of 60 or higher, and look at both ways between 50 and 60.
The reason you try to follow this rule is because 1. a woofer meant to be ported will lack in low bass response if put in a sealed box, and 2. a woofer meant to be in a sealed box will have an odd reponse curve and an extraordinarily long port if you try to work up a vented box for it. This is just my opinion based on my own experience...I don't know if it's 100% technically correct. The pic you showed above has an extraordinarily long port, with five 90 degree corners. I would not build a box with more than one bend in the port...there should be another way to get around it.
The best SQ from a ported box will be a design that uses a straight length of port and has a response curve that has a very gradual curve, and not peaking more than 1.5 to maybe 2 decibles above 0. To get this, start working with a very low tuning frequency, near the driver's Fs. When you work it up and look at it, you'll note that the box itself will not be outputting a whole lot of sound through the port, but there will be some. It will be several db's down from the normal range and the response curve will most resemble that of a sealed box. It is the opposite of SPL, where the port is playing a big role in playing the loudest frequencies and the peak in the response is high in the 50-70 Hz range.
When you're working on the design, the biggest obstacle is box air volume, or total box size. You will always have to arrive at a compromise, but such is the case with car audio.
There are two free box building programs that I have gotten to know, and use them exclusively. One is WinISD Pro and the other is Unibox.
Here is an example that I found in the Unibox database of a ported response that is great SQ: vb_response_soundstreamss-12.gif
The Fs of this Soundstream SS-12 is 32 Hz, the box Fb is 34 Hz, and it uses a port diameter of 6" (which could be configured as a slot instead) with a length of 7". The box volume is large but reasonable at 5.6 cu ft. With this example, you can see that you normally need a larger enclosure and will add more weight to the vehicle to get such a smooth response. But the benefits are a short port length and, of course, SQ. I don't know if this particular sub is even made anymore, but it does work well to show an SQ response in a ported box.
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
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The whole purpose of using a ported enclosure is to extend the low-end output by creating a lower F3 with a rapid roll-off below Fb. Now if what you mean by "sound sealed" is eliminating the peak normally associated with ported enclosures, simply design the system to minimize it. There is really nothing magical about it... 
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