I have been carrying my chins around in knapsacks, fleece bags, and hoods of hoodies for years.
Some will sleep there all day if I let them while others just hate it right from birth.
It does help if they are used to it from birth.
I carry all my kits in a bag around my neck until they are old enough for a run an a table, large cages, and graduate to the floor.
As a result most my chins feel quite comfy amd are well used to it.
Some, as they became adults wanted no more of that, and a few rescues never become fond of it.
As has been said much depends on the chins, but no I have never had one get over heated from just being in there.
I would recommend it over letting kits loose on the floor.
Take them in a bag or bonding pouch, let them run all over you and the chetserfield.
They soon take it as their safe place and will run back in when they are startled.
That;s why I like the heavy knapsacks, they stay opened when layed down.