Reliability on Tubes Amplifiers and Prevention

Tubes amplifiers wired are more reliable than tube amplifier were tubes are mounted on circuit board; however can good ventilation helps prevent to have problems with this amplifier on the boards? This will not prevent to have other regular problems. But a good quiet fan on the side of the amp should kip it cooler so should help to prevent problems on the circuit board.
RIGH or WRONG?
Or the heat produce by the tubes steal will affect the board?
Now in the other hand. What other regular problems will we find on tubes amplifier? And how can we prevent them?
Thank you
Paulo