using dry bags for sandbag training?

Has anyone every used kayak/rafting-style dry bags for sand bag training? Sierra Trading Post has them for $13-49, depending on the style and size. Anyone experiment with them? Worth trying?

To me, they looked like they could be ideal for cardio-oriented workouts because of their size and shape. They're relatively inexpensive, pretty burly (19 oz vinyl), and they have a great roll-and-clip seal that would prevent leaks. On the downside, since they're vinyl they might works better as liners inside a canvas duffel.

On another note, this is my first post...thanks for welcoming another nOOb and for all the helpful info I've been digging out of the forums.

 

my preference for sand bags would be cheap ass canvas army type bags that you can get at any army surplus store. They are cheap, super durable and you can fill them with a ton of sand in trash bags.