I was at a local trailer shop & they had a brand that was new to them called KBS. Can google them, but according to what the trailer shop was saying it was great against preventing corrosion & of course rust that was already present. Also mentioned something that you could brush it on & it was as close to a spray look as possible... well w/o actually spraying it. The price though either in the shop or online was $110 a gallon. It seems pricey, but if it works & you only have to do it once, it may be worth looking at.
You can laugh, But I bought several rattle cans of the stuff to put on my 2004 W900. After the original paint abandoned the frame, I began chasing the rust with regular paint.....didn't last. I saw a 2003 T800 that came out of Pennsylvania, and think I could have poked my knife point through the frame rail just ahead of the drives, that was disturbing.
i did my flatbed with roll on bed liner. looks awesome.i think it would look just as good on a truck frame. johnny