[400 4spd.]

Not playing semantics here, but I want to clarify something. "Base coat" should not be taken literally, i.e. any base coat color. Base coat colors are not moisture resistant. Ground coat may be more accurate. Because the various trunk finishes are suspended in a clear binder and offer terrible coverage, you should spray a "ground" coat in advance that is like a color within the colors of your splatter paint. At my shop we use a coat of epoxy primer (moisture resistant) a few days prior to trunk color. If the trunk splatter contains blue and black, we shoot black epoxy. This gives a background that requires less material to hide. If your final color includes gray, use a gray ground coat of epoxy primer. Doing so gives the illusion of even coverage and will reduce the amount of trunk splatter needed by half or more.
I personally prefer to re-coat the splatter with a flattened urethane clear after at least one week of dry time. A small fan directed at it and set on low will aid in drying. The clear adds durability and prevents color transfer to your spare tire or jack that might be fastened tight against the trunk floor. When using a water based product this is even more crucial. A minor tail light or trunk seal leak can loosen water based products later down the road if not sealed with a clear coat.