Best GTI sleeping setup for road trip?

GTI fam,

I’m doing a 3 week road trip through a bunch of national parks in the South West USA and want to sleep in my 2025 GTI as much as possible to save cash.
For those of you who’ve camped in a GTI or Golf, what’s the best setup? Platform, memory foam, inflatable mattress, or something else?
Also, is it bad for the car to idle overnight with the A/C running? It's gonna be hot and I’m curious how hard that is on the engine and if anyone actually does it.
Any other GTI camping tips are truly appreciated. Thanks!