A bit of a daft question really. Coke cans don't leak because they are for a one off task. Just try try-sealing one!!!!
The only Dev tank I ever had leak was an ancient one 40-50 yrs ago where the only agitation was by a rotary process with a rod through the top and when it was upright. All my current tanks I use, ( 4 x Jobo [35mm & 120] 2 x Durst 35mm and 1 stainless 35mm) never leak provided the lids are put on properly. All it takes is a bit of care.
As for losing temperiture, ANYTHING will cool down if left in a cooler place than where it was when it was first heated up