What do I think?
Based on what I've read about Steven, I believe he would be incapable of the intricate planning required to carry out "the perfect disappearance", by himself.
That leaves me with two possibilities:
1 - Someone helped him. Whether they had good or bad intentions, I do not know. He doesn't seem to be the gigolo type that someone would be willing to financially support in exchange for ... washing windows? Would he stay away from his family for this long? Did he want to be a Basque sheepherder in the Elko/Ruby Valley area? Are there typically ads that say "sheepherders wanted, we furnish trailer, meet up in Anthem Sun City"? That leaves bad intentions. But then, why lure him so far away, when they could have popped him off in the dark parking lot of Kmart, the night before?
2 - He parked there, went for a walk, then took his own life.
I hate this, but I'm still leaning towards #2.
Why:
We have an indication his cellphone was used on Dec 14th to call his voicemail...but we don't know the technicalities of it. Is it possible that someone found the phone, tried to find its owner, it went dead, and they threw it away?
The government doesn't come in and swoop applicants off the street. If he had somehow qualified for a position, there's an application process, references, security investigations and a ton of paperwork. Others would have known he was applying.
If he found a ranch job like Keri Bray, wouldn't that be a step UP from washing windows...and he'd tell his family about it?
Keri Bray, mentally challenged and having no relatives, was able to walk away from the the developmental center in 1986 because things were different. No security cameras. Few missing persons networks. He was an adult. He had no close relatives. Basically, no one cared. There was limited local news (I remember hearing about it...but it quickly faded away).