If it was summertime, the heat could have dried out your "P" trap(s). The odor could be from your grey tank. They can stink almost as bad as your black tank.
Also you need to keep the rubber seal on the toilet wet. The odor could come from a dry toilet ball valve too.
06 Hurricane 34FT WH W20 Chassis 8.1L 120K, Steersafe, Koni Shocks, DIY Trac Bar, Tri-Metric 2025RV Battery Monitor, 4-6V Batteries, Scan Gauge 2, Crossfires, 735W Solar Morningstar MPPT-60, KVH R5 In-Motion Sat, XM Radio, 07 Chevy Malibu Maxx Toad, Falcon 2, Brake Buddy, Escapee