The challenge with the shrinkwrap over the lifelines, is a good snow build up or storm wind can take down the stanchions. I lost all four gate stanchions and bases two years ago, not clear which cause.
I built a deck tent last year, by taking a 40' plastic tarp, laying it over a ridge pole, then cutting the edges to just reach the deck. I then had the edges hemmed and added grommets. The end result looked a lot like your cover, but was re-useable and secured inside of the lifelines.
just another way of doing it.
Certified...in several regards...