Hiking straps flop down? Go to a department or toy store and buy a foam pool "noodle". It's a closed-cell foam plastic cylinder toy about 5' long and 3" in diameter, costing $2-3. Cut a length, slit it, and slide it around the vertical strap, securing with duct tape. Don't use the standard polyurethane foam found in most packing boxes, it's open cell and absorbs water. There's just enough for one boat.

Another Solution

Complements of Rondar:- Attach thin lines of shock cord to the hiking straps and secure the ends of the shock cord to points on the thwarts (eg Spin cleats). The straps will be pulled up and tight