Well, plaid is always a good choice, but other prints that are well spaced and geometric are possibilities as well. We've had some conversations that white was by far the most common color of shirt in the period, but not very practical for farming and dirt. The shirts overall are pretty blousy, although a camp tent does sound a bit big
. Have you tried looking at some of the photos of working men posted on here? I don't have the exact links right now but they have been very helpful to me in helping dh put together his working impression.