In the heat of the summer all we can do is check the psi at each gas stop and check for nails, etc.
It seems to me that by upgrading to a Load Range D tire and a larger size would make sense at replacement time .
Inflate to 65 psi on the load range D
If the tire goes to 50 psi then we still have the same load capacity as a C load range tire .
A few extra bucks to pick up some reserve capacity .
225/75 R 15 D instead of 205/75 R 15 C gives maybe 30 % extra load rating .
Cheap insurance to prevent ruining the trip .