Converting New 115 Volt fixtures to 12 Volt DC is easy.as long as the New Fixtures are of a similar Size . just use the Sockets from Your Old Brass Fixtures to replace the Ones provided in the New Fixtures. while You are at it You might consider using LED 's !
Door Pulls ,Hinges and Recessed Hanles should also not be a problem ,as most of these items are available off the shelf at Home Depot or Lowes!
For those odd ball items that aren't easily located there are spray paints that can do a pretty good job of covering Old with New!
Although We are not quite ready to make the change ,I have been looking at doing the same thing. In Our Coach. I already converted all the incandescent bulbs over to LED 's but haven't changed out the. Brass for Nickel just yet.
Rob & Jean
98 Dutch Star Diesel Pusher ..07 Honda CRV AWD