Not sure what your figuring for the paint, but... 2qt's blue and one qt red should do it. Depending on how thick you lay it on,
most first time paint jobs guys lay it on thick and run out. You only need enough to coat it for colour, two medium wet coats

I'm guessing you already figured out from the botom how much you will need for the top in white... unless you done that already

At least you will have a little red and blue left over for the trailer details if you paint it white to match.
Like the preview look! can't wait to see your progress next.
are you laying the red and blue over white? of just primer ?
Rob