Includes 4 guards that fit in configurable split rear doors, offering passive cooling Middle Atlantic Products standard solid rear doors on WRK, MRK and ERK Series (pg. 35) enclosures are configurable for achieving optimal active or passive thermal management. Fan, vent and filter kits are available to install after laser knockouts are removed from door. Fan and vent kits now available for solid split rear doors. Vent kit includes four fans, 380 CFM Fits in configurable solid split rear doors