If this will be blowing in the wind, I assume it will be blowing in the sun as well. PEX has terrible UV ratings.I'm sorry, what I've been calling 5/8" is actually know as 1/2" PEX. It's actual OD is 5/8". The industry's nominal 5/8" is indeed 3/4" OD, but that is not what I'm using.
Read the 6th FAQ listed in this page. 1 month limit of UV exposure on some grades, the rest get 3 months. I know you will not be running water pressure or risk any damage, but I cannot imaging this thing looking nice after 3 or 4 years in the sun.
Uponor is a PEX tubing manufacturer.
http://www.uponor-usa.com/Residential-Plumbing/Contractor/FAQs.aspx
Apparently there are building codes that require all PEX to be covered after installation so it cannot be seen (or it will not see any sunlight). Also, some postings about building codes that dictate how PEX is handled before installation (when it is unpackaged, where it is stored, ...).