We also have a Tvan with 2 kidlets.
They go on a bunk setup which (just) fits across the back of the hard floor. The window there gives them plenty of ventilation.
Last year we did 3 months in it with lots of packing up and setting up.
With regards to time taken to pack up, I find lots of 'conversations' on this (and other) forums. Yes, the Tvan is quick to pack up and set up, but it's all the other stuff that we tend to carry that takes the time.... chairs, tables, tools, BBQ, plates and cutery, water containers, etc, etc, etc,,,,,,......
After 3 months I wasn't 'sick of it', but was getting a little tired of the process and longed for a caravan setup, but glad we didn't have the weight, given where we took the Tvan.
The kids love it and for us the compromises are acceptable.
Cheers,
Mark