Niloc
sorry no pics but i drafted the following image to help you visualize it. Its in four steps cuz I can't draw 3d.
1) The first top left pic is the plywood slab for the most narrow footprint of your tank (my tank was a 48x48x30 cube so the most narrow footprint was putting it on its side for a 30"x48" footprint)
2) top right - I added three 2x6 across (screw down with many screws)
3) bottom left - I added two 2x6 lengthwise (screw down with many screws)
4) bottom right - I put two 50' ropes through the opening you will have from the different layers of 2x6 wood and once the tank is on, screwed some pieces of 2x6's along the back and sides to keep it in place. Just the weight alone should keep the tank on the sleigh but you can use some straps to hold it down too.
hope that helps.