What it sounds like you're looking for is the Jack-It 2 Bike Rack for A-Frame Trailers # LC429756 which installs on the front of your trailer in-front of your propane tanks.
This rack will do essentially the same thing as what you're looking to do, and it will guarantee that you have enough room to remove and access your batteries since the rack won't even be near it.
If not, then we also have the Stromberg Carlson Bike Bunk Trailer-Mounted Bike Rack Carrier for A-Frame Trailers # CC-275... view full answer...
For your 58" long arms, you're going to need the Replacement Idler Arm Assembly for Lippert Edge RV Awnings with LEDs # LC62ED for the Idler arm, and Replacement Drive Arm Assembly for Lippert Edge RV Awnings with LEDs # LC22ED for the drive arm. view full answer...