It doesn't sound so wrong. Hmmm. First, I'd NOT use the tray method. Neps don't like to sit in standing water. Second, it sounds a little like there isn't enough air flow. I'd see about increasing that - maybe cut the lid back so it only covers about 75% of the tank. Depending on where you live and the ambient humidity, you could have even less; I grow my plants in open air using no terrarium. It's pretty humid here, though.
Finally, you can't trust what the store did with the plants. I'd repot them in larger pots in long-fibered sphagnum and orchid bark and/or perlite and/or pumice. Use about half lfs and half crunchy bits. Stores like Lowes generally sell N. ventricosa or N. x ventrata, and in any case will sell easy, hardy plants, so your temperatures and light should be fine.
Make sure, also that your lights aren't cooking the plants. Recheck the temperature after the lights have been on for a couple hours.
Good luck! Let us know if they die. We can help with that! LOL!
PS: You should have put this in the nepenthes forum. This is in the section for other pitcher plants.