Re:First post and first trailer build
Hello Eman welcome to roadfood, I am not a professional by any means ( other than cooking ) so I can not answer your question ( don't want to give you wrong info ) I contacted several RV stores and have been sold RV's more times than I can count because I go back to them often to get "intell"...no intention to buy but I am learning off their systems on how things work... you might try to visit one in your area if it's not to far away.
Also do a search here for propane, gas lines, propane lines, etc. and see what you come up with I have ran across several articles here about the subject and many of the builds do have pics of their line runs.
Best of luck can't wait to see your build underway.