6 1/2" Tower speakers

I have a set of 6 1/2" Rockford Fostgate speakers that I would like to use for a wakeboard tower. I have been reading about alot of the DIY speaker cans and would like to try this. What size of PVC piping do I need to use with a 6 1/2" speaker? The speaker cover has a 7" OD. I have found a store that sales 6" and 8" pvc pipe, but I am uncertain if this will work. I also have a JVC CD receiver in my boat with a 4 channel output. I already have 4 speakers in my boat. If I add the addtional 2 speakers, can I wire them in series with two of the other speakers? Should I use an Amp? I will probably purchase the clamps from Pro-Werks. The rest of the material looks like it could come from my local hardware store.

Todd,
I made some PVC speakers using 6 1/2" RF's, and posted it here last year using the coupler and end cap for 6" PVC - the OD is exact match to speaker grill. You can either do a search through the archives or go to Bill's (Monster Tower) DIY website here:

http://bierbower.net/diytower/home.htm

for instructions/supplies. Scroll all the way down. NOTE: I tried using just the end cap, but it didn't sound very well, perhaps because of lack of air space. Good luck and have fun.