I want to add a hot water recirc line to my trailer

Myredracer- Personally, I think your solution is good, but could be quite a bit expensive both in parts and time. Since you already have a pump pressurizing your system, why would you need another? I think BigDog's idea is the best. You don't need to do extensive mods and it will simply work. No need to replumb in locations that are a pain to get to.