IMO that looks far nicer than being all over the side of the truck's doors. Very well done, though I agree about going two boards high for the dump bed. More capacity capability and larger numbers/letters.
Are you going to try to seal the wood with anything so that the paint doesn't get chipped/scratched/gouged easily when throwing debris into the back? It seems like it'd be kinda tedious to protect the letters individually to repaint the wood black (and not get any into the letter recesses) so that you can keep the wood looking as good as the rest of the truck.