I always use additional tape as otherwise the edges would peel up and eventually expose the middle of the sensor. I don't recall any particular problems with hot weather, I do try to avoid getting sunscreen on the sensor (and tape - see later).
My solution to the peeling sensors is not pretty but it's easy - I use an ~8" piece of micropore tape wrapped over the sensor and around my bicep/shoulder (depending on which way I lined it up - you only get one shot as it's then stuck in place!), make sure it's not too tight (put some slack around the shape of the sensor before you stick it down onto your arm.)
There are doubtless better/other options, but you might be able to get some tape abroad to tide you over.
Are you using aftersun/moisturiser on your arms at some point before you apply the sensors? I need to not wash the area in question with moisturising body wash (Dove) as otherwise it would fall off even faster (water is fine, I just have to remember to avoid the arm in question when throwing Dove around in the shower 🙂). I also steer clear of moisturiser (in the winter, as I get dry skin) for a couple of days on the arm a new sensor will go on.
