Naps on the go

Hi! I have a 4 month old and we have been trying to go with a possums approach. However she will only nap in a pram after 35 mins (exactly!) of walking. A carrier is better but it’s hot where I am currently and kills my back! She’ll nap in the car but otherwise it’s feed to sleep. Any thoughts on how to acheive more naps on the go? I know it says they take the sleep they need but she gets reallll cranky!