I just bought a 16' Load Trail dump trailer (14K standard 24" sides) and talked to the local Line-X folks about spraying it. First off, the bed would have to be down to bare metal, which means sandblasting it. They wanted $80 per hour to do that. Second, they said the standard Line-X coating wouldn't withstand the normal wear and tear a dump body gets, so they recommended a commercial coating called XS-330, which runs $12 per square foot. That would be something like $2,400 (pre-tax) for my trailer. I wasn't willing to spend $2,600 to coat my $7K trailer.
They actually said the best coating is an industrial version called CU400, but that requires special equipment not all Line-X dealers have.
I really wanted to order mine so I could get it painted, rather than powder coated because many people have problems with powder coating on dump bodies after a few years. It gets nicked/chipped, water gets under it, and it progresses from there until you have to remove it or deal with rust issues. With paint it's easy enough to touch up, but not really possible with PC.
It would be nice if they would powder coat the frames and outside of dump bodies, and then paint just from the rails inward and all of the bed. I didn't want to wait 8 weeks, so I bit the bullet and went with a PC model...I'm hoping that storing it inside will help protect the PC.
Since we all love pics, and while it's still shiny and new:
