There seems to be no more reliable business plan in Seattle these days than selling food off a truck?especially if you're giving something down-home a little upscale twist. And the Spam items at Marination Mobile already have homesick Hawaiians and post-bar drunks memorizing the truck's schedule. For the traditional Spam musubi of Hawaii, Marination takes a giant slice of grilled Spam and lays it over a rectangle of nori-wrapped rice. It looks like a cartoon-sized piece of sushi. For its sliders, the cooks grind up the Spam and bind it with egg, onion, and milk before forming patties, much like making a meatloaf. Throw it on a soft pull-apart dinner roll with slaw and "nonia" sauce (as in "none-ya business"), and you're enjoying a perfect specimen of late-night or on-the-go grub that will turn any Spam-questioning haole into a convert.?Maggie Savarino Thurs.–Sat. nights, Pike Street & Broadway; see marinationmobile.com for location schedule.