How do you ask someone to be your FWB?

Beatrice
So I got out of a shitty relationship about a month and a half ago and I am completely over that guy. I'm going to college at the beginning of August and I really don't want to get into another relationship and then have to leave it behind. All I do want for the summer is a friend with benefits. I want to ask one of my guy friends who is honestly the only guy that I trust not to say anything about me behind my back especially when it comes to things like this. I was going to ask him the other day in person but he couldn't make it. Should I ask him in person or just text/call him to avoid any awkwardness if he isn't comfortable with a friends with benifits situation between the two of us?