Whilst I agree that Resysta may be good for the “cold-wet” environment, I am concerned on the long them heavy load bearing capability. Resysta is ideal for façade and light load applications like decking. For structural applications like pergola posts, we typically will need to use steel or aluminium channels inside the Resysta profile as reinforcement.
Coming back to the Dunnage Rack, I think 200kg of static load is probably within workable limits but I am concerned of sudden impact when loads are dropped onto the rack.
For applications where aesthetics (i.e. the look and feel of timber) of Resysta is not needed and it is just functionality that is required, then I think a straight aluminium rack or even a uPVC rack will workout a lot cheaper. Any idea what is the budget for one of these racks.
This is just my take on this particular application.