Channel letter PSU sizing, what wattage buffer to add?

[ate_mae]

Sign shop question. Customer wants 4ft channel letters, 60 white LED modules.

Each module datasheet: 0.72W @ 12V. Total: 60 x 0.72 = 43.2W.

Do I size PSU at:

• Exact: 50W meanwell, run hot
• +30% buffer: 60W, conservative
• +50% buffer: 75W, expensive but lasts

Client wants 5-year sign life. Tropical outdoor. PSU dies = service call.

Sign industry veterans: actual derating rule of thumb? I usually go +30% but had two PSU failures in 18 months recently. Reconsidering.