Id pick up the DD and put it in the recomended ported box...you might want to tune it a little lower though. They say 45, but it would still be good in 35. I was considering a DD 3515 when I bought my RL-p. Price won in this though. 280ish vs 350ish.
DD has a tendancy to add lots of little costs because they're made in the US. Steel price rising, the fact that they are now making their own yokes on the woofer...and probably the gas price rising will add costs //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif
Both are good woofers but the DD will win in SPL hands down!! I was going to do it sealed also, oh yeah and I was looking at 15's.