Phone number for site requests?

[indimom]

We're booked for the last week of July, 2013. Tent camping.
We have a large tent (16X16) plus an easy up we will be using. Looking at the map, I would prefer the 1500 loop if we can get it (appears to be closer to the pool than the 2000 loop), but I've read that the pads are smaller.

I didn't see anywhere during the reservation process (online through Disney) that I can request a location or note the size of our camping equipment.
Is this something I should call about?
If so, when would I need to do that?

(I did try a search, but could only find conflicting information regarding faxing a request, so I hope there is some more up to date information.)

Thanks so much for any help!