FWIW - If the last known time the Dylan's phone was used (not saying working or anything else) by Dylan was around 8 pm Sunday night.
The next time MR was seen was sometime Monday morning for his errands, he had an attorney appt. so let's say that was at 8 am Monday.
How far can you drive round trip in 12 hours? Pretty far.
So, IMO, if MR was to have done something to Dylan on the drive home, he had 12 hours driving time, heck give it 10 hours, to go anywhere. That's a lot of ground to cover.
IIRC someone earlier posted about the differences between stranger & family disposing of a body. IMO, a family member would be more caring, have some remorse. Perhaps an old favorite campground?