I use the Tbags spacesaver bag It collapses down when not in use and it comes with a rain cover
http://www.tbags.com/touring/space-saver-bag.html

 

T-Bags Roller Dekker comes with rain cover and fits perfect. Don't think they make it any more though.

 

Dekker Supreme Bag
Cost some more but worth every dime it costs.
http://www.tbags.com/touring/dekker-supreme-bag-80.html
Easy on/easy off.

 

I have used the collapsible bag for several years and have never used anything but the Velcro straps to hold it down, and believe me, my wife packs it to the point that it should be traveling in a car of it's own. I do take the carrying strap and wrap it around the rack (just for added security) but the Velcro has always held with no sign of failure.

The bag itself is not waterproof, but it came with a rain bag in the side pocket, actually if I remember correctly (which it's very well possible that I don't) it was attached to the zipper for the side pocket. I know one time when I was loading the bike I needed the rain cover, and my wife didn't know what it was, and had removed it from the pocket, so it can be overlooked.

 

That rings a bell! I think I do have one, but very heavy rain can get in from the underside, hence my black sack.

 

How much clothing can you actually pack in there?

 

I have managed to pack a few pair of jeans and shorts tshirts socks and such to last a week. It actually holds more than i first thought. The trick is learning how to pack it. I typically roll my clothes to take up less space.

 

I realize this is an old post but on the chance someone is looking for a Tour Pac rack bag you might want to consider this . http://www.harley-davidson.com/store/tour-pak-rack-bag . It has been with me on many a long ride . Highly recommended .

 

This is what we have, more than $150 though. It has a rain cover that attaches via strap and Velcro and has its own pocket. The two ends zip off and double as little back packs if you want to go on a hike. The ends also have bottle holders that are in a good spot for the passenger to be able to reach them. Lots of space! Connects via quick snaps and has lots of tie downs on top to connect bungees. For our three week camping road trip this held all our camping gear (tent, bags, stove, sleep pads and rain gear). Ours is mounted on our airwing rack.

 

I use the Kuryakyn Classic Tour bag on mine which is plenty large enough in most cases for us (4-10 day type of range). Bought it for $99. at a show sometime back. Has a rain cover and is lightly rain proof without it. Easy on/off. I like the idea of accessing the bag from the front and both sides since I never remember where the hell I put stuff. We use it for rain gear, quick access stuff etc. on the longer trips and use the tour pack for the main clothing suitcase storage. Side bags for tools,heavy stuff/liquids and other quick grab items. Used to use it on the Dyna for overnight trips before the touring bike came so it has been in use quite a bit since ~2009 and is still in good shape. Has a couple quirks but good bag for the money we paid.

http://www.kuryakyn.com/Products/708/Classic-Tour-Bag