Which tarp or shelter?

I would go with the GG SpinnTwinn.

It is like 2 ounces lighter then the siltwinn, a little lighter then the MLD and a little cheaper then the MLD.

> Question; how much colder is a tarp usually?

When compared to a 3-season tent, it depends a lot on your setup. Most tarps give you a lot of wiggle room to adapt to weather conditions, which can work for you as well as against you. The learning curve just involved learning how to optimize it for your comfort depending on the weather. :)

When I did my first tarp camp, I camped right alongside a roaring creek, with the open end of the tarp facing into the wind (yes, I know that's not a good idea for normal practice, but I wanted to try something, which I'm coming to…). I set up my MLD Serenity under the tarp — mine has a full silnylon front. It got pretty cold there as the sun went down and the katabatic breeze kicked up — it was blowing down the narrow canyon and right into my camping spot, and that water was quite cold. Once I zipped up the Serenity however, I was fine — and even the Serenity trapped enough warmth to be noticeable when I opened it up the next morning.

If I'd made camp like you're supposed to (better location, not facing the tarp into the wind, etc), I wouldn't have needed the Serenity for warmth, but it was a good experiment.

Without a bivy, you will definitely be colder in an open-end tarp vs a mid-style shelter. Not sure I can quantify, though, Aaron. Maybe 5deg or more? A stiff breeze will definitely be noticed.

If you aren't a cold sleeper and/or carry a warm bag/quilt, then no big problem.

I am Ok with using a bivy, my sometimes backpacking partner though is not real keen on buying more gear so he would likely be without one, thus my possibility of no bivy in my consideration.

I had a p.m. to consider the Trailstar if not wanting to use a bivy, it has more setup configurations which is useful for weather.

2 Bivys + large tarp + mosquito netting + ground cloth = probably more weight than a BA Fly Creek 2 person tent or a TT Double Rainbow.

Correct, something I am considering although I won't use or need a bug net and I don't need a full groundcloth really either.

The Gossamer Gear Spinntwin is currently unavailable because GG is having trouble finding decent spinnaker. It appears that the one I recently received was one of the last available!

If you have plenty of $$$, GG has the same design in cuben fiber. If you don't, it's also available in silnylon. The MLD Grace Duo is a similar design.

I haven't yet tested my Spinntwin to see if I can survive nasty storms without a bivy. I'm getting mixed advice (i.e. everyone I ask has a different opinion!) so I'll try to simulate horizontal rain with a garden hose in the back yard. It will be just me and my dog under the tarp, though. After a preliminary living-room setup, the tarp looks as though it would be an extremely snug fit for two humans when snugged down in storm mode.

I personally wouldn't try camping in Colorado or anywhere else in the Rockies or Cascades during mosquito season without a bug net. Maybe after mid-August!

I have the same issues that Eric mentioned: Spinntwin plus ground sheet (needed for gear and dog even if I use a bivy) plus 2-person bug net (for dog and me) plus one-person bivy altogether weigh more than my GG Squall Classic tent, which is just the right size for me and my dog. That doesn't include the extra 4 stakes needed for the tarp. The only way I can save significant weight is without a bivy and without a bug net. In other words, I'll be using the tent until mid to late August and the tarp (only if it works without a bivy) after that.

I use a SpinnTwinn plus bivy. No ground cloth or bug net (bivy!) so its pretty light. I use a trash bag as a pack liner and just throw my pack in that at night.

I wouldn't want to use that as a two person tarp if the weather was nasty. Unless it was with a significant other. It can be less than spacious if pitched low for a storm or wind.

I have a Spinntwinn and a Trailstar. I like both a lot. The Spinntwinn provides suitable protection for a solo hiker without a bivy but I think it'd get a little cozy and cramped under it to provide suitable protection from windblown rain for two without bivies. I use my Spinntwinn as more of my spacious solo shelter.

The trailstar is quickly becoming my favorite all-around shelter. It's got plenty of space for two underneath it, even in a low storm pitch which provides excellent weather protection. Then when the weather is nice, you can raise it up to a higher pitch. Very versatile and reasonably light for a spacious two-person + tarp-like shelter.

I like the simplicity of a bivy but could never find one big enough.
So I made an XL version. 1.5 lb and bigger than most 1 man tents I've tried.
So much easier since I can sleep anywhere.