I am putting a box in my trunk and l was wondering what you guys think l should do...
i have (2) 700w rms 10'' subs
or (1) 800w rms 1000w peak sub
which would sound better?

ill be building a custom box also. so which ever l choose to go with will have its own specific box and size.

It is Real hard to decide on the RMS rating that you provided because so much is overrated anymore. l would usually say go w/ the single 12 but a sub that is 800 rms/1000 peak is not something l am familiar w/. You should have listed the name brands and models.

I'd say go by quality..!!

Go with the 10 is because a subwoofer that only peaks at 1000w and RMS at 800w can not be a great quality subwoofer. The 10 is will sound great in a sealed enclosure and you will love it more. 1400w is better than 800w in my book, and 10 is are better in some cases than 12'' subwoofers. Good luck

the 10s would sound a lot louder in side the car but the 12 will probably travel further l do not know what kind of sound you are looking for but to be honest their might not be that much of a difference and it will be a lot cheaper to find a good mono block amp to power the 12 rather to find a good multiple channel amp for the 10 it up to you