I live in the tropics in Australia. I had an ileostomy for 10months last year. I found that my 2 piece system didn't stick for as long in the summer when it is really hot and humid here. I think the humidity was the problem. Make sure you really dry your skin before applying your products. I always carried extra products in my bag in case of leaks. But dont keep them in your car!! The sun and heat degrade them and they wont stick at all. I'm sure this is an obvious one but I tried to use the disabled toilets whenever I had to change my appliances when I was out because you have access to a sink and a bit more space.
Hope that helps the person wanting to know about ileostomies and summer.
Good luck!! Enjoy your summer