I had a small shed/cabin to install some plumbing into and purchased this tool to crimp the rings, so didn't buy it exclusively for working on the trailer.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
The cost is cheap enough that after purchasing several sharkbite fittings, the crimper becomes less expensive so you can use the crimps and the fittings. I found that Lowes carries the full line of fittings for the 1/2" PEX along with the rings.