Can be a challenge some help from a buddy is in order if you can ..otherwise place shelter upside down atop some saw horses.
Couple tips ..
Use a drill a size or two smaller then the bolt/screw used to secure the hyfax ..this way the threaded bolt screw through the hyfax then shelter tub this will allow the hyfax to stay in place until you can get the bolts on
Use a 5 gallon bucket of hot water to soak the tips of the hyfax ..this will make it easier to made the bend in the curve portion when attaching to tub.