To answer your question about the tent - we just got back from the Fort last night and we stayed in a premium site in the 400 loop. We have a 45 foot motorhome and it fit onto the site with no problem. However, there was absolutely nowhere on our site for a tent. First off it wasn't big enough, and second the only place where there was any sand was a narrow patch on the side of the site where the hookups were. There is no sand pad in the back like there is on the full hookup and preferred sites. I did see a tent on a premium site, but I didn't see how they had it staked down. That site had a popup and a tent and with the little popup the tent fit easily. Again, though, there's no way we could have fit our 45 footer and a tent onto our site. Our site was a decent size, and seemed pretty standard for the premium loop, although there were sites in our loop that were longer (and shorter) than ours. Enjoy your trip - we're hoping to be there for part of that time; I made our reservations a couple weeks ago.
BTW, I see from the list posted above that 400 is a premium loop, but not a pet loop. I saw at least 3 sites in the loop with pets on them - I'm not sure whether the people in those sites didn't mention their pets or whether FW permitted it, but I suspect it's the former.