Here comes an out-of-the-box thought I just had....
Perhaps he concocted some chlorine gas to subdue her/knock her out. May be how he got her out of the house without any sign of struggle. Firemen have gas masks as part of their gear so he would be unaffected. Could be a second round was needed and that's why the hotel smelled as well... and it wasn't BM who was laying on the bed for a bit. This could be easily determined on hotel security video... which begs the question - Did Barry take an ice chest into the room at some point? Seeing one on security video that has since disappeared would be damning. Also could've had her locked in a container with the towels and just needed to refresh them or rinse them out after he was done doing something off-site.
100% spitballing conjecture... but, hey...
ETA:
It's not unheard of... and according to this article -
Firefighters handled an incident fairly recently.