I bought a 400 watt converter for my camper van, and it was only around $40. That would power up quite a few lights, but if it were me, Costco and Wal-Mart sells the new miniature LED Christmas lights that are really low wattage, lightweight, and DON'T produce ANY heat! That's what I would go with! You could probably get away with an even smaller converter with the LED lights!

I'm actually thinking of doing the same thing with my car!