My WRAP1C is running a customized version of 1.2b8 as filtering bridge 
and traffic shaper in front of my firewall. The ambient temperature 
often is 28 to 30°C these hot summer days but the system runs stable.

The WRAP1C is in the original alu box with its cover on. No cooling like 
a fan or so around it. The CPU load is between 5 and 15% (only, on a
4 Mbit/s symmetric ISP connection). I use the 18VDC plugin power supply 
as supplied by PCEngines.

So, if you are using a regulated power supply, try to crank up its 
output voltage towards 18VDC. Because if your PS is "linear" regulated 
and not "switched" this will reduce its power dissipation and there it 
produces less heat. This may help to stabilize operation if your PS 
tends to become "soft" with increasing ambient temperature.

The power supply onboard WRAP is of switched type which is very 
efficient and produces little heat to convert the 18VDC down to required 
3.x and 5VDC.

Rolf