They could simply, after months on the road, have realized there were some things in storage they wanted and had room for on the rest of their trip that they’d left behind but now wanted. Supplies for the road trip. There are also some ~things~ that can be used in a somewhat “therapeutic” senses for couples (though illegally and not classically therapeutic without guided therapy). There is research being done on these things, if you catch my drift. Maybe they felt their relationship needed a deep-dive connective experience and had some of these things stashed away in a storage locker. I certainly wouldn’t want my parents to ship that to me, either. I am not supporting or discounting that something like this, (not even necessarily this but to your point of “what could they not want shipped?) necessitated the visit to the storage locker. I also think that retrieving something from the locker doesn’t take 5 full days (7 days including travel). It was likely only a portion of his trip home that was devoted to that. Unless he picked something up during that trip and brought it back to SLC with him, and that something became involved in her death, I don’t think that the trip is necessarily related to what happened to Gabby a week after he retuned. However, the mystery of the odd timeline surrounding the 2 weeks between the Moab DV stop and her death, including this trip, is what makes it speculative that it’s related in some way. I just don’t see how it’s related unless her COD relates to something he retrieved from the locker (weapon, toxicology, etc).