Your attachment method is fine as far as durability is concerned. The highest stressed point is where the water-pipe is clamped to the PVC tube and the carrying-plate. That pipe will crack just beyond the hose-clamps.

Personally I would suggest a more substantial 3/4" pipe the entire width with 14mm nuts welded/brazed to the ends for the axles to screw into. Then have an additional 14mm nut to lock.