I used Zero Rust, on the Booms of the Holmes W45 Wrecker I just sold. I used the spray can version, & it was about 6 years old, & still holding up. I've also used POR 15, & as mentioned it's more toxic, & fades more with sunlight exposure.

Spanky Hardy
Collector Of Fine Old G.M. COE Trucks & Antique Holmes Wreckers

1948 Chevrolet 5700 COE Holmes HD W35 Wrecker
In the Stovebolt Gallery
More pictures on Photobucket

1950 GMC 250 1-Ton
In the Stovebolt Gallery