Yes that is right. I have a modified motor and truck connection that uses the truck as a heatsink. The surface is very large to transport the heat better to the truck. See attached photo. And I uses for me 4 wheel drive so that I get really quickly enough speed. At the low RPM the motor gets faster warm by current as by higher RPM. At higher RPM you have more like the AC than DC values of max current. So that is the reason why some manufacturers of in wheel boards reduces the current limit at low RPM.
But there is a little tip to get more heat disperse to the truck by using the normal Jacob motor: verify that the gap between the motor and truck is absolutely clean and tight. The holes from drilling the torque bolts can cause a large gap e. G. Or the truck is not manufactured clean so that there is a little bit too much aluminum at the shaft...
And you must put cooling paste like arctic silver on the shaft and between the truck and motor connection. And the alignments crew is to be secured with locktite! When this screw lose then the motor will be very soon too warm.
But is is real recommend to use 4 motors that brings very much... Then the motors will stay cool and you have real fun with it. Hillclimbing is no problem anymore. Even when you are heavy like me.
The PLA can handle this temperatures then. Maybe it depends on the PU resin manufacturer too. From which manufacturer do you have ordered the PU?