"The cabinets for 2245's should be 37" x 27" x 17" and should be made from 1" particle board if you don't mind the weight. If weight is an issue, then use 1" plywood and choose a good quality stock that is free of voids. The port should be 4.25" x 7.5" and 7.5" long." Those are the internal dimensions, and you need to brace the heck out of them to avoid panel resonance.

Dale Gernert (Robert H on the JBL forum) has alot of experience building sub boxes for JBL drivers. Here are some thoughts/info from our correspondence, concerning 2245 subs... (BTW, JBL's professional enclosure guide says for a single 2245 a 10cu footer tuned to 30, being 32x26.1x22.6 with 75 sq inches of vent area or 6 four inch ID duct tubes.)
Here is JBL's box they used, which I think is 8 cu ft if I recall.
http://www.jblpro.com/pub/obsolete/Low_Frequency_Enclosures1.pdf

"The 2245H in an 8 cubic footer is the classic fourth order butterworth maximally flat alignment that's for sure. If you are going to be moving these about, then 8 cubic feet is plenty enough to be hauling about unless you have some roadies to help :-)"

"The ONLY problem I have with the 2245H is it's enclosure volume requirement. If your listening room can support two 8 or 10 cubic foot enclosures then you are good to go. JBL went to great lengths designing the B460 (a home sub with a 2245) to make it as pleasing to look at as possible because most consumers would really balk at having a 4518 style box sitting in their living room. I have quite a bit of experience with factory B380's and B460's. My personal opinion is they suck. I mostly blame the BX63/BX63A for that. Additionally, the B380 at 4.5 cubic feet is simply too small and tuned too low for the 2235H without the EQ of the BX63/BX63A, the B460 is tuned too low for the 2245H without the EQ of the BX63/BX63A. Consumers must have felt the same way........

From experience, a 2235H in a 5 to 5.5 cubic foot enclosure tuned to 30 Hz and crossed over using a non EQ'd network such as the 5234A romps all over a factory B380/BX63. We installed many 2235H's into custom home theater systems. From experience, a 2245H in an 8 to 10 cubic foot enclosure tuned to 30 Hz and crossed over using a non EQ'd network such as the 5234A romps all over a factory B460/BX63. We only sold one set of 2245H's for a custom home theater system and this couple had us build the enclosures into the wall. The depth of the enclosures went into a service hallway that ran along the back of the listening room. The end result was spectacular. The 2245H can move so much air with so little effort and with minimal distortion it is truly the ultimate home subwoofer. It needs a big room to operate in though and a big enclosure to live in."