For what it's worth --
One on my friends has a similar problem - he backs his skidsteer onto the trailer with chains run from the back of the skidsteer, through the D rings on the front of his trailer, and laid out towards the back of the trailer. After backing on, he ties the chains to the trailer's rear D rings (without binders) then pulls the skidsteer forward (towards the back of the trailer ) and applies all the tention he can. After shutting down the skidsteer, he chains the front of the skidsteer to the trailer's rear D rings, pulling all the slack he can.
Effectively he's got all four corners tied down, though he only uses 2 binders. This puts a good strain on the trailer's rear D rings, but I'd assume no more than if the front chains weren't run back. Under a stop the rear chains, with binders, take all the load, as normal.
He reasons that with high sideboards, the skidsteer isn't likely to go anywhere, even if there's a bit of slop in the rigging - unless, he flips the whole rig.
Depending on the room you've got to work with, you could also do this by running a chain from one front D ring, across and behind the skidsteer bucket to the other D ring and pull back, or even put a binder in the middle, behind the bucket lip. All this depends on your room to maneuver, and weight distribution.
If your problem is that the skidsteer is too long for the trailer, meaning that your rear D rings are too far forward to provide a good angle (scope) to prevent the skidsteer from from sliding forward, can you load it with the bucket tipped up against the headboard, so that both the bucket edge and the bucket lip are tight against the trailer's front boards? I'd think this would gain you some room, though it would shift your weight forward a bit.
All this is speculation - without seeing your exact problem, I'd hestitate to recommend any specific solution.
