I have a lot of rust on my underbody....what do people do? Is there a spray we can use to just treat and cover exposed or rusty metal areas?

 

Gotta get rid of the rust before you paint anything. I believe thats what "undercoating" is for from the dealer, to prevent this from happening. Gotta get that rust blasted off, or lasered off then apply, well anything rust is cancer man, literally!

I believe bedliner is a good spray to use after removing the rust, like Herculiner

 

Forgo the rubberized liner, just go with something like Fluid Film, or in your case because its Ontario, Krown Rustproofing. Personally, I feel its by far the most effective way to slow/prevent undercarriage rust from getting worse. Its essentially an oil that finds its way into every nook and cranny and creates a barrier between the metal/rust and the elements. It needs to be performed yearly, but has done a great job helping slow the rust on our 4runner

 

Thanks... I came across corrosion free... Something the Canadian military tested and gave high ratings. It's also in oil form.
I already have rusts and don't have the energy and time to remove the rust. I guess I'll just spray the oil stuff and hope it does its job.