The eviscerated dead body on the frozen lake has a greenish-looking face. In the snow and cold, there would be no advanced decomposition withing a couple of days.
David's large, deep facial laceration doesn't bleed.
When David smashes the gun rack to access one of the rifles, as he lefts the rifle one can see that it's a lightweight replica, likely plastic. The way he handles it, the gun clearly not of a regular gun's weight.
When the creature's hand comes through a removable plate plate on the floor of the trailer and rips out David's throat, it's unclear how the creature knows the position of his body, or that it can push up this plate to access the victim.