Over the years, I have found that different DMV offices have different... habits. When I registered Millicent, they wanted receipts for the RV equipment I was installing. So I brought them copies of the reciepts for the Thetford RV toilet, and the shower stall, and the foam rubber mattresses, and the several water and waste tanks, and 12 V water pump, and some 20 foot lengths of steel, and some lumber I bought a long time ago, and a few other things.
I think I paid a fee based on the amount those receipts added up to.
That was it.
But I strongly recommend you paint the bus, even if they should forget to enforce that when you register it.