For Premium Luster, I would consider Premier Print Shield. Does a very good job and will give you basic protection from fingerprints and light scratches. However you will have bigger issues. http://www.dtgweb.com/shop/product.php?productid=25020&cat=0&page=2
This will help, but with any print of 48", you will have handling issues, if you don't at least mount it, and frame it. Epson Luster will scratch in a heart beat while handling, and while moving it you will most likely get a v Crease and ruin the print. Luster and any paper coming off a roll will have curl and this alone makes working with large prints tricky. I am referring to just handling from the printer, to mounting board for normal framing. RC paper, (resin coated) which is what Epson Luster is, will take a long long time to get all the curl out. You can use tools like the D-roller but there will still be curl and once you roll it up to transport, you will put curl right back in. With a print of this size, you will need to roll it up for transport, and this will also give you a chance to damage it.