Just had mine mounted on the side of my house. My Phase III was previously mounted on the side as well. Vinyl siding too, although we have the "shingle look" stuff that its more prone to issues with expansion and contraction. Never affected it with the Phase III, but it was located in a shaded area. The 5LNB is around the corner in an area that gets sun and shade during the day.
Time will tell I guess, but I dont see it being an issue. The installer actually started the job assuming it would go on the roof, but (luckily, maybe) it was windy the day of the install.......he got up there and said it would be much better to put it on the side of the house, situated such that its pretty well blocked from the wind. Ended up with even better line of site than my Phase III, and also ended up aligned better too.
-Chris