PEI or Polyetherimide is the thin plastic film stuck to the build plate of a Lulzbot.
It has some great properties for sticking to and holding the printed model, and yet is able to be easily separated from the completed print.
The strength of a Polycarbonate filament, particularly with larger prints, the 3mil PEI film that is standard on a Lulzbot can be lifted right off the bed as the plastic cures. One solution is a thicker PEI such as 1/16th of an inch thick. Another solution, or so I have heard, is an aluminum build plate. I have not tried that.
To get consistent prints, you need to control the environment. This includes humidity (below 15% for many filaments) and temperature. I use a room dehumidifier to hold the humidity at 30%, which seems to work fine for PC-MAX. I find that when printing PC-MAX, the temp inside the enclosure without a heater runs close to 100F since the bed is heated to 100C. This makes a big difference in print quality over room temperature without an enclosure.
With a heated enclosure, you can run the temp up to 50C (122F), but Lulzbot says above that and you risk serious damage to the printer (although there are some strategies for getting around that by also adding cooling for key components).
The reason that no one including Lulzbot sells a heated enclosure, is that Stratasys owns the patent on it. Which means you pretty much have to build one yourself.