Thanks for the input. I think I meant to say 80 watt RHP, not 120. I use a 40 watt on each side of my T8 and it does fine.

And yes, I plan on keeping the lids on and keeping them on industrial shelving for the time being.

The tubs haven't yet arrived, but seem to have just been redesigned by IRIS. If the lids are as sturdy as the ones to my sweaterboxes, I think an RHP will mount up fine. My thoughts for mounting was to use a strip of wood behind the lid to screw the RHP screws into (something maybe 1/4" thick by 3" running the length of the RHP behind the screws).

Space heater isn't really feasible as my room is huge and takes a ton of heat (plus my power bill jumps by $400 if I try to do it for a month).

Worst case scenario if I can't maintain temps is to move them into my walk in closet and use a space heater. I know two RHPs would be better to control the temps, but it's much more expensive. I may start with the 80 watts and add another 40 watt to the cool side if I can't get a good gradient.