the la400's don't couple well past 3 or 4 per side. we are doing larger events up to about 5000 folks so the la's aren't nearly enough. they are awesome sounding horns, don't get me wrong. i can just sell them and easily upgrade to dual 18's with cash left over. (by the way i only have 2 left if anyone is looking) plus with the 18's i get more pop instead of wump. although both are desired, a little processing and i'll be set.
i have a full function woodshop, and have made many cases etc. before, just never used it to do a production run of cabinets. that's why the screws comment set off a few questions, i love using wood glue and crown staples. yeah it takes a little more time and work, but you get smooth lines and a great bond. rarely do any staples back out, and i don't have to worry about stripped threads or anything when repairs may be needed... thanks
edit: as far as the side by side, i have done it. we do mostly outdoor camping/ music festivals and what not, with the opccasional indoor concert thrown in for good measure. i had one where the client grossly underestimated his attendance, and with only 2 850 tops and 2 la400 bottoms per side it wasn't nearly enough low end. (the tops covered well, but we threw up another on top for the long throw.) the client had 2 sb 1000's nearby (it was a theme park) so we added 1 per side on a 5k... the difference was night and day. but together was something else. since i had the subs on an aux i sent that back into the console and ran a split matrix. one send for the horns, another for the 1000's. combining the two was amazing. i had the punch and pop of the dual 18's, plus the warmth of the horns.
i'm just more a fan of the dual 18's in large format situations.