If you can store the ramps under the trailer, down the length of the trailer. Using C channel as your guides to support the ramps under the trailer as well as when you pull the ramps out. Your ramps have round bars, weld brackets to the end of your trailer the round bars would sit into to support the ramp, I would have it as you pull the ramp out the round bars on end of ramp would drop into brackets at end of trailer. Then once you are done using ramps slide and pin the ramps back in place to secure them.
do You know if the sell the brackets to weld on the trailer or is that something that I have to fabricate
These would be custom fabricated brackets, doubt anyone would have off the shelf brackets you could purchase. Check with www.speedwaymotors.com for brackets.