carrying spare propane (20#) while traveling

Yep. Carry two 20# tanks every trip. They sit in milk crates in a basement bin. No issues at all. I use them for the portable fire pit and for our outdoor stove/oven combo. I also have at least 4 of the small individual-use Coleman lantern/stove LP tanks as well. Other than being loose tanks (mine are secured in the bins from rolling around and falling over), what makes it any different than the mounted 30gal on-board tank? Portable tanks are on the front of most every pull-behind camper, and many more than that go up and down the road in transport trucks to retail outlets every day.