Household wall paint "will not" properly adhere to the plastic end caps, or to the vinyl clad aluminum interior, unless you properly prepare the surfaces.
The vinyl walls must be cleaned and then sanded with at least a 150 grit sandpaper. They must be positively sanded, not just a scuffing.
Likewise, the plastic headliners must also be cleaned and then sanded the same way as the walls.
If you do not sand those materials correctly, in time, the household paint will simply peel off, along with the primer.
A primer coat, for longevity, is a must.
Caution. The cheaper the materials you use, the more likely they will fail, over time.