Access with slides in is a layout issue. It's not a MH vs Trailer issue. Yes, getting one where you can access fridge, bathroom and possibly bed is a great advantage.
Driving down the road the heat/cool isn't that big of an issue. None are sealed that well and the wind blowing by will tend to keep it fairly close to outside temps (with the hatch covers you can leave them open really helping).
The dash Air/Heat won't handle your typical motorhome space. If you are running the generator the whole time, you could do the same with a trailer (they can be had with built in generators also)...but really not a big issue.
If you are just making a quick stop and will be off in the morning, as long as the site is reasonably level, yeah, you can leave it hooked up, so you can head out quickly in the morning.
Really unless you can live without a TOAD (which brings it's own challenges), there is very little difference traveling with either option.