Looking for Single Axle Brake Line Kit with 20 Foot Feed Line  

Will Im surprised your brakes are on the rear axle. Every trailer I've seen they are on the front. Regardless. I would recommend against running the flex line in the trailer frame. Every entry and exit point increases the risk of chafing through the line. Running it outside the frame allows you to regularly inspect the lines for chafing or sun damage. If you have any other questions let me know

I agree with Tom B, would not recommend putting these lines in the frame…unless you protect them from chaffing! Metal lines inside are ok, even then I would protect with something like hydraulic hose sheathing, and still inspect regularly.

Wil S, I just replaced the brake lines on my tandem axle trailer. It also has one axle with disc brakes. The name on the brake line kit can be a little misleading in that the lines service only one axle, regardless of whether it is a dual or triple axle trailer. If you have one axle with brakes on them, this kit works. You can buy the 20' kit, but make sure it includes the bends to run the main line to a point where the fitting for the branch lines reach in the rear, as well as how it is routed through the center bar of the trailer. As for running the lines inside the trailer, I would run them on the inboard side of the rail with the hardware they supply. Just make sure you drill a hold for the rivets to the correct size so they are not loose when "popped" into place. If you do need to run inside the center bar, which I recommend, then it's likely you'll need to get the line out of it on the top side to connect to your master cylinder. If you do, use a rubber grommet to insulate the hole, which is typically used in automotive, marine, and other electrical applications. Just make sure you match, not just the hold diameter, but the thickness of the metal. You can find them on Amazon or McMaster Carr.