If your sites are not lasting long enough there are a few different things you can try. I like to put a piece of tegaderm/IV 3000 with a hole cut out. Here is a picture of what it looks like. I use a 22mm hole punch like this one and it's about the perfect size to cover the adhesive but leave the plastic exposed so you can clip your tubing back into your site.
You can also use Skin-tac, but it's quiet sticky. I use it on my dexcom to get the full 10 days out of it.
To put it in perspective I'm 6'4" and weigh about 275 and work outside in the south (I sweat alot) and rarely have problems with adhesive not lasting.