how tall is the passenger? My wife is about 5 ft tall and said it gets hot. Did find the dog house was not reinstalled right, fixed it and was some help. Since she is short she uses a foot stool to keep feet up and off floor. says it really helps. Can get for $5 at some dollar stores or cw sells for about $20!
Talked with another guy and he said he added the insulation, more external muffler exhaust shields etc and still has issues. Said he added some flex tube from the AC to direct air to floor area. you might want to give it a try.