This will make a very nice painting indeed. I think the size of the van is fine, as it is less the focus than the landscape itself in my mind, but that spark of red will definitely draw the eye.
I would just crop a bit off the right of the photo, shift the tree to the left, and leave the van about where it is after having snipped a bit off the photo. Too bad it's an 18x24 in dimensions. . . this is such an expansive scene, I bet it would look amazing as a panoramic.
What you presented in the adjusted image is pretty much what most of us would do I would think.
As for the subjugation that Virgil mentions, I generally agree with the assessment, though I feel confident you are fairly familiar with composition overall. More eyes never hurt though.