I used a toy hauler for 2 years while my son was young and took naps. It was a life saver on those long track days. For naps, I would just throw him in the bed (or on a couch) up front so I didnt have to put the “garage beds” out during the day.
At night, we would leave our karts out under the awning or an ezup. Never had any issues. If it was supposed to be super windy or something like that, I would put the kart covers on and then put the EZ up down over top of them and stake it down or tie it to the generator or something for added security.
Depending on the size of your toy hauler and the size of your karting operation, you can often slip the kart in and still sleep in the garage, as well. We did that a few times when we were going to a race a long ways away and had to stop overnight on the trip home. No issues with fumes or anything. Just drain your fuel before you put the kart in and clean everything before you put it away.