No problems! I was looking at the rubbermaid tubs and from what I can see on their site, they are pretty decent tubs (material wise), but again you will pay a bit more for them. Right now my ambients hover between 75 and 80F, during the winter they will drop to the mid 60s and when we hit tripple digits I wouldn't be suprised to see them climb to the mid 80s. My reptile room is a modified garage, I added double wall insulated doors, redid all the seals around the doors, double paned window, with sun blocking shades and plumbed AC/Heat into the room and installed 2 ceiling fans. So I see that the temps are stabilizing, to 80 during the day and 70 at night, however with just a thin wall of metal I know the temps will fluctuate with the room when it is mostly air space in there, if that was the base of your permanent cage and it was filled to the brim with dirt then they heat loss wouldn't be as drastic.
On a side note what type of lab do you work in?