Excellent point. LE said that the truck was seen several times in the neighbourhood. Yet, we have only been shown the one photo of the truck. Therefore, there is a reason for that. That reason could be that there were items in the back of the truck.
Also, LE asked family members to come to the house and see if anything was missing. These missing items could be blankets, mattresses, bookshelves, rugs, whatever else DG could have used to cover up the victims. I recall a photo of LE bringing a blanket back from the landfill.
So, hypothetically, DG made several trips from the victims' home to the Airdrie acreage, each time covering up evidence with the missing items.
Then, once he finished, (sorry) he used his chemical knowledge to dispose of bodies and evidence, followed by burning. IMVHO (in my VERY humble opinion) there are no bodies. So really no use in looking for them. There is just forensic evidence to find, DNA, very small things.
This also explains why DG did not skip town. He needed a few days to dispose of bodies and associated evidence.
Given his past behavior, after committing a crime, he would have ran. He may have planned to do the same this time, but wanted to finish off his original plan first. After all, he's a meticulous planner, as we have seen.