I'm thinking about picking up 2 85lb Launch Pad Bags. Are they any good since they are only 85 lbs each and not like 540? Do you need a pump to fill those up at first? I want to be able to carry these around in and out of boats and might want to keep the water in the bags at all time.
I have a light boat and have one 350lb sac and 4 85lb launch pads. They are good for me because I can move them around and balance out the boat. They only take about two minutes to drain and about the same to fill so you should consider is lugging an 85lb sac around worth the time you are saving by keeping it full. The handles are sturdy enough to move them on a regular basis.
Give your sand bags a liberal wrapping in duct tape (2 - 3 layers) and they won't leak. The tape also makes them more solid for moving them around the boat. Wrap tightly. Purchase the plastic type bags if you can.
Before wrapping the bags, take some webbing and make a sling around the bag. Cover all but about 8 inches of the webbing when you wrap the bags with tape and it will make an excellent handle.
Total cost is about $7 - $8 per bag, each bag weighs 50 - 60 lbs depending on the sand bags you purchase.