I`d do the outfit, then just the car (or t`other way around), which will give you your train weight, and if you subtract the weight of the car you will have the weight of the van, although not perhaps as accurate as some pedants require.
It will at least tell you what your axle loadings are, an important point missed by manychasing the ounces.
as explained elsewhere, if the weight isn`t in the car, it MUST be in the van, it can`t disappear!