When cooking on a griddle, mass is your friend. You will have better heat distribution, and not as likely to have hot spots. That is one reason that SS frying pans have not worked so well- they are often too thin. Some have a thicker bottom, and perform better, but I'll stick with cast iron.
Commercial griddles are sold in 3/4" plate, and are milled flat. They are wonderful to cook on, but, of course, at 30 lbs/sq ft, they will outweigh your bumper! I have no experience with 1/4", but at 10 lbs/sq ft, it may still be a heavy beast. SS will be about a pound heavier in 1/4". And a lot more expensive, of course. I do not see the advantage in this application. Rust? Bacon helps most everything!
I have seen, and handled griddles like the one pictured, but have not cooked on them. My concern is that they will not remain flat over the long term and many hot/cold heat cycles. They also seem thin to be used on what is often an undersized heat source like is common on camp stoves.
My opinions are informed by well cooked pancakes, waffles, and eggs. Master the slow cooked pancake, and you're well on your way to getting up early just to feed all your friends.
You will likely find in the end, that you need to mod your truck as much as the friends you go with, so choose them carefully. (AndrewP)
98 Tacoma, X-cab, purple, $10 sliders, purple,too. 235 85 16 Toyo Open Country AT, fresh body work by AZCAAROKCO rocks, trees, succulents, etc.
04 Isuzu NPR HD, custom box
05 KLR 650