Shelter choices depend a lot on location and season. I know down here in the SE, from late spring to early fall, I don’t want to sleep on the ground. In some locations it’s wet, at certain times ticks can be overwhelming. I much prefer a hammock setup. Additionally, with the heat and humidity, you can overheat in a smaller bivy tent.
From fall through early spring, a tent isn’t a bad option and provides a more enclosed shelter from the elements.
I like a hammock setup as my rain fly is just a tarp and can be used as a stand-alone for a ground shelter; for me a hammock setup is more versatile (and comfortable).
Sil-Nylon is about the best value for performance and robustness when it comes to tarps. If you want more than just a hammock fly, I would opt for a traditional rectangular shape, long enough to cover the hammock (10-12 feet length-wise). Some hammocks have bug nets built in, others can have them added…a big consideration during the buggy-months.
For colder weather, a good 10x10 tarp can be configured in a pretty robust shelter. Add a ground pad and bivy bag and you’re well insulated and protected from the elements.
Another nice option is the Lawson Hammock. It’s a spreader-type hammock that can also be setup just like a ground bivy. I like it, but still prefer the versatility of a traditional rain fly. Even still, I will often switch from a single bivy-type tent to a hammock as the seasons change. My three "tent" choices are a Snugpak Ionsophere, Catoma Raider or an OR Alpine bivy paired with a small rain fly.
I too have the Gunslinger II pack and if you can fit the shelter kit in a tubular stuff sack, it would easily carry under the bottom flap outside the pack, freeing up room inside for other gear, yet quickly accessible to get your shelter up fast if needed.
ROCK6