Mine is a double axle. I was playing around with it and first noticed the flex when I used the trailer jack (port side). So I used a floor jack on the starboard side and noted that the roller centered on the bow with no that much pressure on the floor jack. So I started by taking the spare off the starboard side, which corrected about half the issue. Now that I've mounted the spare on the port side it's centered. So I'll see what happens after a few tows with it like this. I suspect that it may flex the other way, but who knows. Either way seems like a BS way to jimmy-rig these trailers. The last time my dad was down, I had him inspect the trailer for structural issues. He's a welder with a lot of experience building truck beds from the frame up, and custom trailer setups for hauling rigs for the oilfield industry. Any way, he said "besides the light axles, lack of support beams, and thin-gauge steel throughout (he especially noted the the winch tower and bunk support brackets, but said that the rails should have been thicker or reinforced more), it's fine". Not exactly a ringing endorsement....
To clarify, my dad's comments were based on hauling a 4,000lb load (boat + fuel + gear).