Remember, there are many other ways to make this or any type of hologram. Feel free to experiment with the geometry. If you can, make an isolation table for your hologram set up. However, it is not essential for a successful exposure, but it will help you obtain brighter holograms in a noisy environment. This acts as a shock absorber.
Some people make a sandbox and float that on the inner tube.
The table top should be rectangular at least 3 feet by 4 feet. Longer is better than wider. You can also work on a hard top table or a concrete floor. Aim the laser through the lens . This will spread the beam out like a flashlight.