I have put about 6000 miles total with a coleman lantern basically laying down (maybe up at 30 degree angle) in a large box with all the other gear and have not broken the mantles yet. I couldn't believe it the first time, I was ready to replace them at the first camp and was in a hurry just threw it in the box and it worked so I've just kept doing it. Alpine loop in SW Colorado, all over GSENM washboard gravel roads, even I40 from Amarillo to Oklahoma City. I try to sort of lay it on a tent or something softer but I know it takes some hits. Would not believe it if I didn't experience it.
Edit; this is a propane version and I leave the tank attached, but wouldn't think this would make any difference.