Inconsistent Authentication Prompts in CRM/SharePoint Integration

In a CRM 2013 environment for one of my clients, there are a handful of users who regularly utilize the standard SharePoint document integration from CRM. They say some get prompted around once daily and then are fine, but more will get prompted every time they want to interact with or upload any document. Questions on this all seem to have answers that point to this article: http://blogs.c5insight.com/Home/entryid/245/Tips-to-Avoid-Login-Prompts-in-SharePoint . But, they've insisted that the first to steps (Add IE to local security zone and manually create Credential Store entry) don't work, and noticed that the 3rd step regarding the hotfix is not applicable because it's only for Vista (7 comes with it included). They are accessing over CRM over an IFD URL. Any ideas?