The Wirepath Rubber Grommets are compatible with the 30" and 42" plastic enclosures.  There are (3) 1-3/4" openings on each end of the enclosure that these can be installed for additional protection once the knockout is removed.
Wirepath™ Plastic Enclosure Grommet Kit - 10 pack
The Wirepath Rubber Grommets are compatible with the 30" and 42" plastic enclosures.  There are (3) 1-3/4" openings on each end of the enclosure that these can be installed for additional protection once the knockout is removed.
10 Rubber Grommets Included
There are 10 rubber grommets included in each package so you have plenty of protection to work with.
Complete Protection 
Rubber grommets attach to (3) 1-3/4" openings on each end of the enclosure for additional protection once the knockout is removed.