Put mine on the inside all the time. Even with normal "EPA" cans, I rarely get vapours if I screw them tight.
For all people who are concerned with safety - fuel is safer if it's secured within the vehicle's frame / chassis. If you have them in the back, and you're severely injured in a rear end accident, you may not be able to move while your fuel cans set the entire vehicle on fire. You'll never be hit hard enough to rupture a gas tank strapped in the rear seat area. If you do, you have bigger problems to worry about...
For long distance travels, I yank the middle seat of my Explorer, which creates a big open floor space. I place the heaviest stuff in a layer: two Trojan T-105s, 20 Gal of water, and 10 Gal of gas. That's 360 lbs flat on the floor, your CG doesn't get better than that! Only thing on my roof is my Tepui.
For all people who are concerned with safety - fuel is safer if it's secured within the vehicle's frame / chassis. If you have them in the back, and you're severely injured in a rear end accident, you may not be able to move while your fuel cans set the entire vehicle on fire. You'll never be hit hard enough to rupture a gas tank strapped in the rear seat area. If you do, you have bigger problems to worry about...
For long distance travels, I yank the middle seat of my Explorer, which creates a big open floor space. I place the heaviest stuff in a layer: two Trojan T-105s, 20 Gal of water, and 10 Gal of gas. That's 360 lbs flat on the floor, your CG doesn't get better than that! Only thing on my roof is my Tepui.