Do bugs get inside?

I stayed in my new AS this past weekend and was freaked out when I went to bed and found a beetle and a spider. They may have come in during the day when I had the screen door open. But was wondering if bugs can get in very easily when everything is shut. If so, what does everyone do to keep bugs out, like if you are storing the AS out in the country. I was extra freaked out because we had found a kissing bug earlier that night outside the AS. They are scary. Google them if you don't know what they are.