Living in BC tarp's are a must have ..Some where in my web travels i came across a fellows idea for a cover. it is basically a pole system that attaches to the trailer to give you a main center ridge. ropes to the ground on the off side and adjustable poles to the RTT's entrance side. I have mine done but no pictures of it set up. here's a couple of rough paint sketch to show basic idea.
I used 1/2" square tube with 1/2" round tube to make the poles they basically plug in to each other.
I used 24' of tube to make the main frame and 18' to make 3 poles.
here it is on trailer stowed for travel.
If you want more info let me know .. the tarp used for this is 12x20
Cheers