Download the 'Water Planes' sample project located in the 'Learn' tab under 'Engine Feature Samples' section. That project contains a transparent water material.
Just a heads up: We're asking that your diorama only contain the driver + vehicle, no additional characters or vehicles. Small props, though, are fine.
thanks for the critique kurt! Going to call this done. Went for a different kind of handpainted style. Kept a bit of realism, but still contain the handpainted look.