I have just made a strap type boarding ladder.
I used a heavy duty storm strap from my caravan awning and 2 x pieces of 1.5" abs pipe.
It adjustable and threads through the handle on the tube to keep it in place and secures to the eye for towing the ringo.
It does take a bit of practice to use but works well and was cheap.
The other idea I was going to look at was a ally ladder that is used to get in the kids bunk beds in the caravan.
Very light weight and strong,Spot on the correct length,But ideally would need a curve putting into it so it fits round the tube snug.