Hi
Weight not being a big issue with me I found that as single pack liner a nightmare as they never really matched the pack shape so just annoyed me. My approach is to use a multitude of bags as it makes for keeping things in order. Got the idea when backpacking around Europe and it worked a treat as less stuff to get lost in a mad packing to catch an early morning connection after a long night out. Downside is you can wind up with a kilograms in sacks.
My personal favourite is a rectangular bag that has a Therma-rest type valve. I fold the clothes up in it and then sit on it to remove the air and then close the valve. Works a treat as it stands up vertically in the pack. Also it makes a great pillow

I tried a lighter weight solution that used flyweight nylon type material and an Event base so you could squeeze the air out. Trouble is it would re-inflate quickly so bulky stuff like a down jacket would fill the pack space while packing.
The Sea-to-Summit compression bags made of Event waterproof material for sleeping bags are wonderful. If you need to compress a sleeping bag then for not a great weight penalty you get a waterproof solution as well.
As for pack design it is interesting with stuff. Hilleberg tents pack up short so can be packed horizontally while other brands pack up narrow but long so require vertical packing. Also say OP packs are wider so well suited to horizontal packing.
Generally in my packs sitting on top is a Kathmandu day pack (200 grams) containing wet weather gear, PLB, first aid kit (own drybag), AAA headlamp and toilet supplies (own dry bag). Under this goes the tent. The day pack contains what I need if a day side trip turns into a evening/night dash.
Oh and yes, I use traditional canvas packs and they do a remarkable job remaining dry so if I do chuck a top in I do not need to put it in a dry bag, providing that I can handle the possibility of it getting wet. Means in the layer on then off days I have less mucking around.
In all my trips I yet to have a wet item even when a water bottle exploded in my pack.
Cheers
"lt only took six years. From now on, l´ll write two letters a week instead of one."
(Shawshank Redemption)