Yaoi where the two guys have sex on the train, or in a car? Something along those lines.

On the back of a moving truck:

http://www.mangago.me/read-manga/taiyou_to_himitsu_secret_and_sun/mi/mi_chapter-1/

Hmmmm...I don't know you've read this or not but here, "Sex on Train":

http://www.mangago.me/read-manga/sweet_inomoto_rikako/an/sweet-inomoto-rikako--chapter-5.html/12/

You mean like this? o3o I only remember this one.
http://www.mangago.me/read-manga/himitsu_no_kuchizuke/an/himitsu-no-kuchizuke-chapter-3.html/2/

My vehicles sex list is exactly what you are looking for http://www.mangago.me/home/mangalist/29085/

Hehe thanks!

http://www.mangago.me/home/mangalist/70799/

http://www.mangago.me/read-manga/sekaiichi_hatsukoi/mh/v04/c001/63/