Thank you for all of the input guys. I feel like I have a decent handle on the options available now and I just need to make a decision on which one to use. Here are the options I'm considering:
1 - do nothing
2 - roofing felt
3 - poly sheeting
4 - Drylok
5 - 0.5" rigid foam insulation
6 - Dricore
7 - SuperSeal All in One Subfloor (http://www.superseal.ca/Brochure/All...e_Subfloor.pdf
Right now I think I'm going to go with the SuperSeal. Middle of the pack pricing, should definitely do the trick in terms of vapor barrier with breathability, and is only 1/8" thick. I like the Drylok idea too - I used a TON of that on the walls at the beginning, but I'm hesitant to put something on the floor that I can't remove with relative ease. I have heard before that Drylok can cause issues on some floors.
Originally Posted by TMcG
Regarding your comment above, how did you go about calculating the size / number of vents in order to use the riser as a bass trap? Is there any relationship between the size / number / position of the vents vs. the size of the riser base? I would be very interested in learning your process on this.
TMcG - I purchased the Pro Theater Layout Service and the Helmholtz resonator/bass trap was part of the plan. (FYI, I think the layout service was the best money I have spent to date.) Unfortunately, I'm no help on that question - I'm just following orders!
EDIT: Just saw Floyd's response - My subwoofer (Danley DTS-10) has a pretty big knee around 54Hz. I believe the trap is designed to target frequencies in that range.