Neat game! Would definitely play a post jam update, there's a lot of fun mechanics to be explored here. As others have pointed out, an attachment grid would've been swell; not just for the train cars but for the turrets and chimneys as well. It was hard to tell at a glance how many attachments I could actually fit per car, and whether it was a fixed amount or if I was able to squeeze more on with clever placement. Also, the ability to detach cars would've been cool, that way you could shed excess weight if you lost too many engines - at the expense of any turrets you have attached.
I would also say, make sure the shading on your assets is facing the same direction. You probably put a random rotation on the trees for variation, but it doesn't really work with the trees that are only shaded on one side.