If you are looking to do it all on one machine and move it from place to place then a strong laptop is the solution.
As mentioned before, cooling is the Achilles heel of working on heavy renderings, I know that feeling of waking up in the morning to find a shut down machine due to overheating instead of a in depth rendering.
I now have a big, angular, matte black, heavy, Asus Gaming laptop. The laptop has never overheated even during multiple day rendering sessions with all threads maxed, it has two big fairly unattractive fans at the rear that carry all the heat away, which on the very occasional time it sits on my thighs means that there is very little heat felt.
I am not looking for any nods of approval when I flip up the top of my laptop in public. Actually the looks are of shock, 