need help !! I will be building this enclosure this weekend but the size needed will be about 29" width will this affect the sound in any way. It will be going in the trunk of my daughter honda accord, my sub is a stereo integrity v1 mag d2 and mmats 800.1 amp. any suggestions.

I wouldn't know about the DB212 but my regular DB for 10" drivers was too long (on purpose) And when I brought it back to the size it should be, it sounded noticeable better and a bit lower.
But that's just the other way around of what you are asking of course.
Here is the thread about that:
https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1186436463/26#26

I too have a length issue. My space is 31" at the max. I'm going to use 3/4"mdf, so my thought was whether or not it needed double thickness walls on the port end and maybe not quite double thick on the sealed end. It's that or loosing an inch from the chamber.

I have not bought the plans yet, still in the planning stages, so my thoughts are based on what I have seen in the photos. But I'm not going to pay for something that will not fit in my setup.

Will probably buy a couple 500w rms subs from Sundown to run with my 1000w rms Orion amp to put in it...