when I used to do a lot of bicycle touring or packing I cared about size and weight and other things like that 
now I am in a truck/SUV hauling a trailer 

 I care more about comfort with a huge bag for the whole family current one is 80x81 inches the size of our bed on top and having a heater and hot water and a refrigerator and a stove a pett toilet inside the tent room for emergencies and the little ones midnight run 

 and all the nice amenities that my family loves also and makes them more willing to go with me 
 
not knocking the idea of really nice bags but I guess to me they were more important when I was having to haul them on my person and storage was a premium etc.. 
winters I had a Moss tent for summers a cheap sierra expeditions the moss was overkill for hot weather and weighed a lot more 
my summer bag was some decent square thing that worked mid season was a really nice light kelty and I forgot the name of cold sleeping bag ? marmot I think ?? 
so my personal thoughts are choose a bag for the job and a hardcore backpacking mummy type for a RTT system is so overkill 
again just my thoughts 

 and not saying others who think its not are wrong 

 to each his own 
on a side note I think it was marmot who had those bags that were a pad system on bottom and you could get dif thermal tops for them ? 
that as a super cool design I think would be killer for RTT use