Here's an inexpensive fixture I built. It uses an LED panel and a card holder I bought at the Dollar store. The card holder comes with a glass lense so, for under-hood use, you may wish to discard that. What I did was cut a piece of 18 ga aluminum to replace the cardboard backer on the card holder. I screw the aluminum sheet to the surface, mount the LED panel, and slide the rest of the cardholder with the lense onto the aluminum. One 48 SMD panel will light up an RV interior. For underhood, constant on, I'd choose an LED panel of 8 or 12 SMD. THat will keep the current low.