Since I plan to sell some of my cels/genga/douga, 
I will be taking them with me again down to my 
university campus. But my room stays pretty cool 
and I keep them flat in the top closet shelf or 
if they fit, i might lay the cel book in my 
safe/trunk for keeping. But usally I let my 
roommate know that I'm into collecting art and 
they don't give me the weird eye when I've got 
them laid out sorting or scanning stuff at the 
computer labs. But for me, the cels are pretty 
safe....its just the trip down there that is the 
hardest when packing things in your car and 
finding a safe place to lay the book and the car 
does get hot a little from the windows, so I 
usually layer some beach towels over to protect 
from heat/light.

but if you have some really valued cels that you 
are not selling/keeping for life, its best to 
leave them at home.

I bring mine to trade/sell or just have a show me 
in person with other collectors which happen to 
attend the uni or live in the area.