Can I get advice for best practices dryhumping?

Novice (M) here, I was dryhumping my girlfriend in missionary, but I couldn’t get comfortable propping myself up on my tensed arms and legs while trying to keep our privates in contact (I realize now I should have used a pillow for that part). But I was wondering, how do guys place their arms and legs during to keep them from tensing up and distracting?

We also tried having her sit on me in the backseat of a car facing me, but I couldn’t figure out a way to get comfortable since even though she’s really light, my thighs took all the weight and contact so we didn’t make much contact between private areas. How do people make that position work?

Any advice would be appreciated, thanks!