Camped here last October and had a good time. Sorry, I don't have any pictures of the pavallion, or remember where it is, but the park has a ton of campsites and they're all fairly suitable, though you may want to bring your own tarp for rain cover over the picnic table at the campsite. They also have screened in campsites, so, that might be an option.
Looking at the map of the campsite, I don't see any mention of the pavillion, unless you mean the dinning hall, and it doesn't look to be adjacent to campsites, so there may be some walking/transporting from the site to the pavillion involved.
Campsite map: http://www.tpwd.state.tx.us/publicat...p4505_090d.pdf
Park Facilities and Fees: http://www.tpwd.state.tx.us/spdest/f...alls/fee.phtml
Hope this helps.