Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If I understand your question you are looking for some way to keep the Oak stand off the floor, perhaps in case of a wet floor?
You do not even have to attach the 2 x 4 to each other. Lay them down flat (the 4" side lays on the floor, the stand will be lifted 2" higher) where the Oak stand touches the floor, then VERY CAREFULLY set the stand on the 2 x 4s without moving the 2 x 4s. You can even put plastic or wood shims in there if the floor is not level.
If you want it to be higher, you can stand the 2 x 4s on edge. When I do this I cut the 2 x 4s square, then screw them together to make a box. No mitered corners. In a basement, who cares for perfect cabinetry techniques? If you want it to look pretty good, then make the front board as long as the stand, and set the end boards inside where you won't see their cut ends. I do this to make stands for 45 gallon tanks, 4' long. It would work just fine for a 75 gallon tank when used in this way.
This will not stop the Oak stand from getting wet, if that is your goal. The wood 2 x 4s will wick water up from the floor.
If you want to prevent this you need to use some kind of water proofing. For example, set up the 2 x 4s to lift the stand off the floor, then put pond line over them. That way, any water that is wicked into the 2 x 4 from the floor cannot pass into the Oak stand. Note however, that if water falls to the bottom of the stand it will be held by the pond liner, not allowed to flow away. So this is a 2-edged sword: It can help if the floor is often damp, but can be a problem if you spill water from the aquarium.
In the green house where I keep a lot of tanks I have some up on concrete blocks. This also can wick the water up from the floor, but does not seem to cause problems so far.