I recently purchased the BPL pack liners. I put it in my pack and it fit all my gear nicely, but it seems awkward to get a good seal at the top. What have you found that works best, especially when the liner is quite full? Thanks

When I use pack liners I typically don't put everything in my pack inside the liner. For instance my cookset and food bag (with vacuum sealed food) don't need to be in the liner. This allows ample material at the top of the liner which I can roll down and then tuck into the space between the pack and liner. I then set the items I don't need waterproofed atop the rolled-down liner, close up my pack and head off.

This is all well and good assuming you want your food and cookset at the top of your pack. For my packing style it works well. Outside of the pack liner is my food, pot, stove, rain jacket (if carried), et al.

Same as Sam. I usually only have my sleeping bag and clothes in a liner sack.