[serious][relationship]Asking friend for benefits

Heres a little background info: -ive started talking to this girl since march -she moved here 2 years ago -asked me to take her to beach this summer(in the beginning of summer) -i don't see her a lot, we text like 3 times a week or so -she hangs with a group of girls that I'm good friends with, they don't see each other very much because of work scheduels -she likes my body -even though she has girlfriends she wanted to go to beach alone with me -she smokes marijuana and i asked her if i can try it with her sometime this summer. -she likes to tan and relax

Anyways i took her to beach last week, we went swimming a bit, tanned and ate peanuts. Ive noticed couple signals, i don't even know if they were signals but, she would splash me when I'm relaxing in water then i would grab her and put her on my shoulder and throw her in deep water(shes short n light, I'm tall and strong). Sometimes i grab her boob or ass accidentally while throwing her and thats when the benefits idea came to me. After swimming we talked about things like her stories with weed and parties then the kinds of people she would date. She popped the dating topic out of nowhere, she has ADD so i figured that couldve caused the topic to be mentioned. She also said that the next time we go to beach we could blaze before. I said alright why not. Then she went home with a ride from her dad and i took the bus. We left off with a simple bye and talk to you soon. The day after i messaged her saying that this was fun and we should do it again soon. She yeah we will.

I don't want to be in a relationship with this girl but simply add some benefits to the friendship. Ive never done this before so I'm curious to know what others opinion is on this. I was thinking that next time were at the beach, i would grab and kiss her in the water and after that i would open the benefits topic when we're tanning.

Tl;dr need opinions on how to ask for benefits.