This is a bit like asking how long is a piece of string. I'm not sure what the limits are for the cabin zone temperature indications, but 47C is not unheard of in an Australian summer on a 744 EICAS screen. It doesn't take long for the temperatures to rise with all the lights and video systems turned on and the packs off. The hottest place would either be in the crew rest above the toilets in the aft zone or in the cockpit (lots of glass and lots of lights), but there are no plastic floor strips there. In the cabin, the temps can go from high teens in flight to 40+ in 30 minutes to an hour if the packs are turned off straight away. Fortunately, the window area is generally small in the cabin (although I hear the 787 windows will be larger), so you won't get as much radiant heat as in a car. You also have an air gap between the outer glass and the inner window for insulation.
These plastic strips are a pet hate of mine. They are always coming out of the floor tracks (the cleaners routinely dislodge these with their vacuum cleaners). The plastic is almost impossible to cut to size with normal hand tools. The strips are difficult to insert into the floor tracks, especially if the insertion part has been dramatically cut to allow for wiring and chair leg tie downs. This leads to the eventual breakage of the insertion part.
Also, the strips are not always high enough to go above the carpet and some of the larger video harnesses (but I guess you have to weigh this against the pax tripping over them).
Not being able to see the insertion part when you're putting the tracks down makes it difficult to find the floor track. If you are having trouble getting a track down, you don't know whether to apply more pressure (with a size 12 boot) or keep fiddling around with them (trial and error), more gently, for long periods of time.
Humidity levels would only be high on the ground with lots of people on board (with the packs off). Or if the aircraft is parked in tropic regions with the doors open... Just check the weather charts for places like Singapore
I assume the strips have to resist 100% humidity (in the form of spilled coffee, etc)
Hope this helps.
Rgds.
NSEU