@bigAl2 Thanks for getting back to us and thank you for making us part of your adventure!
If you are interested in a 20 liter dry sack you can find the Sea to Summit Lightweight Dry Sack - 20 Liters here. These dry sacks all have a roll-top style closure to them. There are plastic rings on each side of the buckle so when you close it you can easily attach a carabiner in order to hang it.
In terms of a dry sack for your clothes, we definitely recommend making sure you have some way to keep your clothes dry on the trail. A dry sack is a durable, reliable way to do that, however, you can also get by with a trash bag lining the inside of your backpack as well. Trash bags can tear easily, however, so you'll want to bear that in mind.
Lastly, we'll see if we can find someone who has experience with the Wonderland Trail. In the meantime, please check out the book by Tami Asars (a former REI Employee!) Hiking the Wonderland Trail. We reached out to her to see if she had some advice to share and she is currently through hiking the Colorado Divide Trail and will not be back until September!
When are you planning your hike?