"The spark should never die". Well, there's "should be" and then there is reality. Most people's busy lives get in the way of spontaneous sex and longterm familiarity dampens the desire. But to answer your question, I'd say van or RV since you carry your own private horizontal space with you. In the other transportation methods it has to be searched for.

yup van or RV, security is important to me. I'm pretty sure we're going to be majorly distracted with our... trysting, and I don't want to look up to find an unexpected audience. If I want an audience; I'll sell tickets.

I know a couple who used to love to do it in the back of their car. Then they turned 50, with their various aches and pains, it just wasn't that comfortable anymore, which ate into the naughty pleasure factor. They don't have car sex anymore.

My point is that people fantasize about having sex anywhere and everywhere, including in vehicles. Those fantasizes are fine. Enjoy them. And sometimes for some people living those fantasies can be lots of fun. But often, a hot fantasy morphs into a cold and not very erotic experience.

If you want to have sex in buses, trains, and RVs, fine. But it's also fine not to.

We do it in the car, truck and on the Harley if the mood strikes, did it on a train once after seeing the scene in Risky Business with Tom Cruise.. it was hot!

I am not a traveling sex person. LOL. Maybe a sex in different location person, but not in a vehicle. Just not my thing.

Things can get interestin' in the back of a cotton wagon, but it's mighty itchy.

Yes it shure would but I did not mined it.