There's a knot which i use all the time. Ok, it's slightly harder to undo, but it's a damn sight easier to tie!!!
tie a slipped over-hand knot, with the standing part going away over the load, and the working end forming the loop to the tie-down. You'll be able to sweat this down plenty.
form a bight in the standing (blue) part of the rope, so the working end (red) is on top. take this behind the standing part and pull a bight through the loop (green). either hook the loop over the tie down, and sweat it down, or preferably, use it to feed the working end (red) back through after passing it through a rail, hole etc.
I always do it the second way, as it's easier to work with.