Locked? No. Keep it from opening on right hand turns? Maybe.
Got bungee cords? Or, picture hanging wire? Both available at Walmart.
Find a quiet parking lot somewhere with a 4" curbed sidewalk at one side of it, that looks like it sees little to no foot traffic. Preferably with a wiiiiide sidewalk, with no obstructions on the side away from the parking surface. You'll need some room for error.
Back your Roadtrek up to the curb at a 90 degree angle to the sidewalk with the back wheels just touching the parking lot side of the curb. Using the throttle with great discretion, and still in reverse, give the engine a little gas and see of you can get the butt of the Roadtrek to back/bump up over the curb and onto the sidewalk. This gives you the clearance to get undeneath it and figure out where to attach one end of the bungee cord or picture hanging wire underneath the drawer. Don't attach it to anything hot, like the exhaust pipes/muffler. Run the other end out from uunderneath and attach it to either the fridge vents or the water heater (after removing the cover).
It's about the best MacGyvering I can come up with on short notice. I see there's not much clearance to get underneath those beasties, like my 2002 Popular. Once you can get underneath, just use something to keep the drawer from sliding open on right hand turns. If you use wire, consider wrapping it with something to help protect your paint/fibreglass.
p.s. Flyer's solution isn't bad either, but not as much fun as mine.