Bill was kind enough to send me these pictures and advice, thanks Bill!
1st Pic is of two styles of diffuser base. Top one is using a child's snow saucer note the connedtion underneath. Typically the disk membrane diffusers have a 3/4" threaded fiting for the inlet port. For the bottom picture, he cut the end out of a barrel, mounted in on a tire and ran air in through tread of tire. Tire adds weight and acts like a sled and unit can be pulled into smaller ponds (1/4 -3/4 acre) with a rope. Leave rope atttached o base so it can be pulled out later for cleaning. Barrel base does not alow muck to move up through the tire when diffuser is operating.
The 2nd pic is inside and outside views of a water heater "drip" pan" as a base, but any other sinkable flat material, or tray, or saucer will also work. Personally I would mount it the opposite way shown in the picture. i.e. Bricks on bottom and diffuser on inside of concave portion so rim forms a low wall around the diffuser and helps keep out muck and sediment.
You want just enough weight to hold it on the bottom because you periodically need to remove it and clean it. You don't want it too heavy. Keep in mind that the membrane when under pressure will inflate somewhat and tend to be more bouyant.
