Which of the LEMO F Series panel mount receptacle have seals and which do not?
The EH_, HE_ and ED_ have a front panel seal. The EG_, EC_, EE_, PE_ and PB_ do not.

 

How can I achieve an IP68 Rating with LEMO's K&E Environmentally sealed connectors?
LEMO publishes a rating of IP66/68 for LEMO K&E Series connectors.
There are 3 sealing points on a typical mated pair.
  1. Seal between the plug and receptacle
  2. Seal between the receptacle and the panel
  3. Seal between the plug and the cable

IP68 is achieved for points 1 and 2. The connector to cable seal is highly dependant on the shape of the cable, therefore it can range from IP66 to IP68.

 For complete details, please see LEMOs IP66-68 Rating Reference Guide for K&E Series Connectors.