Hi, and welcome to the forum.
We have been truck camping for over 20 years now. On our fourth truck camper and 3rd truck.
We rarely take the camper off the truck. Mainly because the camper doesn't make traveling around that cumbersome. Now that we are retired and will be mostly full timing we may drop the camper if we are going to stay for more than a few days. Not sure how often that would happen. We tend to move around a lot.
As far as pets. We travel with 2 dogs. Both are elderly and do fine for several hours unattended. Campers are insulated living structures and shouldn't have shocking temperature swings over short periods of time. Just running the vent fans the inside will not exceed outside temps normally.
That being said we have set up our new camper up to be able to both heat and cool the camper without us being there via the factory thermostat. The heat is provided by the onboard propane heater and the cooling is provided by our inverter and batteries running the roof mounted air conditioner. Both can be run far longer than we would ever leave the dogs alone in the camper.
In general we feel most comfortable sightseeing with the camper and dogs, limiting our hikes and other excursions to under 5 hours.