just ordered a sea to summit light weight dry sack, 35l for $27 with my dividends from rei
sea to summit 20l is $24

but just saw the sealline 20l for $14 somewhere else. thought that might give me more options to spread the gear out, instead of having a lot stuffed in one bag

besides the size,
is there much difference between the 2 brands that you have noted,if you have used both brands??
thank you.

I trust either brand, I use some small Sea to Summit dry bags to keep emergency items in, keep them dry ya know, as well as their eVent dry compression bag for my sleeping bag. I've used SealLine products for years, Cascade Designs has been around forever, Thermarest, MSR (waterbags), and Platypus are among their brands. They oughta be able to figure out how keep a seam on a bag water-tight.
There's something to be said for 2 - 20L bags, helps a bit with organization and finding things in a pack. (although field organization ain't my strong suit)