Hi Cerius,
We grow bicals here in Boca Raton, Florida, but they are in a greenhouse. During the summer the sides are rolled up so the humid breezes can come thru the shade cloth. The top is covered. A lot of people down here successfully grow Nepenthes in screened-in pool enclosures, but they are mostly hybrids. Bicalcarata, like most species, can be a little finicky about conditions. Luckily, if there's any place in the continental US where bical can be grown outdoors, its Florida! What Swords and Beagle said is good advice, except here in summer the sun is extremely intense, and will dry out a concrete patio quicky. This means very low humidity in an otherwise humid climate, especially during mid-day when temps are high and humidity is most critical. Also, our balmy breezes can sometimes get a bit too strong, and will dry out a plant even when there's a high relative humidity. Monitor the conditions from sunrise to sunset before situating your plant.
As for winter: when those cold fronts push through, the humidity drops dramatically, quickly. In a matter of a couple of hours conditions can go from near perfect to 60 degrees F with a humidity of about 38%, with a nice stiff breeze from out of the north--not good for lowland Nepenthes! Put them in the bathroom after running a hot water shower.
Also, we grow our bicals in pure long fiber sphagnum moss, and we overpot. They have huge root systems. Our big female is five feet across and lives in a five gallon pot. The mix you are using should be okay. I know other growers who use a similar mix sucessfully.
Anyway, just a few more helpful hints!
Trent