I have not used it for a truck bed, but I have made furniture out of it.
If you want your truck to be a display piece with a pretty bed it would be fine. If you want to use it as a truck, the poplar is going to take damage pretty fast.
Poplat has a Janka hardness of 540. In contrast:
red oak - 1290
black walnut - 1010
heart pine - 1225
Ash - 1303
Janka hardness is a measurement of how much force it takes to press a 0.444" steel ball halfway into into a plank.
