2018 3500 EXT
Good, I do not like the compression 90 fitting that comes with the Propex. I used the flare fittings & flared my copper lines. Best to soapy water test even a temporary install.I'm not using the compression 90 degree fitting that came with it. For now I'm just fastening a flex dryer hose with a 3/8 flare 90 to 1/4 male NPT, then NPT/BSPT adapter. I got the yellow tape for the pipe thread fittings. Later I'll route copper pipe when I have the time to do it right.
For intake pipe routing, my propex is near the wall, so it comes down between the edge and the main front to back floor support. Seems like I'll have to cross that support with the intake. That will cause the intake to go up again a bit to attach to a crosswise support. If I go straight back I run into the suspension springs.
If you are looking for ideas/comments on your Propex install photos of your intended installation would go a long way (I know that is hard to do underneath the van). You can always “tweak” the intake & exhaust if you are not happy with the 1st install. Just do not shorted either tubes.