Specifically looking for tips on how to keep your wits about you when doing payroll when your company has employees that are constantly traveling...
Mandatory timesheets for all employees. WHERE are you working? WHAT are you doing? Do we bill someone for this time? Do not include just the travelers but everyone not at home office. Or even everyone including home office. I have had employees in 42 states at one employer and have some employee complain that we got their state wrong for the past three years (and just now got around to telling someone). Do not assume anyone will tell you anything if you do not ask.
Not the question but do not assume that anyone in HR will keep track of visa issues. You want to maintain a list of ALL visa people and talk to them (email is good) quarterly to make sure nothing changed.
Are they in the Transportation industry or just constantly traveling on business? If the former you may be able to use the "Amtrak Re-authorization Act" exemption which allows taxing only in the resident state. If the latter, then What David Said.