Depends on tightness of trousers - if they're cargo trousers, with fairly bulky pockets, and you're not out in dark trousers in bright sunshine for hours, then should be OK. I never found any temperature problems to carry my metal insulin pen in cargo paockets of army lightweight style olive green trousers when working as a country park ranger. Howover, I did once break an earlier plastic pen in the same conditions. So, a rigid case may be required. Depending on your work situation, it can be important to have pen and meter with you at all times, especially if you work on a large site and / or several sites. If driving, you need meter with you, and leaving a pen in a vehicle in sunny weather can mean it would get hotter than next to your leg.
You need to work out big picture of your situation - sorry I can't be more specific.