building a fat sac

So I have this old waterbed mattress, I think it's a 'full' size, so a little bigger than a twin, smaller than a queen. I'm also getting a new boat cover this spring, and I was thinking of cutting my old cover into a rectangle and then sewing it into a tube as a cover for the waterbed mattress. I realize the mattress will be way too big for the cover, and it will probably be folded and creased and stuff inside the bag. I'm sure it will be hard to make sure that there is water evenly throughout the mattress when emptying, so does anyone have any suggestions for making emptying it any easier. Will sticking a length of hose into the bag help? Any input would be greatly appreciated.

dude if you are that desperate to not spend a lot of money on a sac just go buy some waterbed tube sacs i got 2 for my boat to add a little weight to the front of the boat only cost 23 bucks the two weigh about 210

I'm building a fat sac too, 1 cheeseburger at a time!

I would say that Shoe Goo is going to be your best friend. Tough and rubbery.

Skiing made me board,
Lyle
Chrome Dome Industries

I bought some heat-sealable nylon fabric from a place down in washington ( Seattle Fabrics i think ) and am going to try to make some custom sacks for my boat. People use this stuff for dry bags and float bags for kayaks mainly, but it's nice and heavy material. You just use an iron to seal the seams. If you watch for a sale, you can get enough for about 4 - 5 sacks for 15-20$... If they don't work, at least i'm not out too much! I'll probably try to make an outer bag out of cordura or somthing for a bit more durability... Any hints/tips/ideas would be appreciated too.
B