Kinda would like a old table that you insert leaves to the center to make it bigger with the basic top is in two sections.
You could do it with a few pieces of plywood. The two basic plywood parts making the top would have cutouts for the stack and either holes or slots for the cold and hot water pipes. It just depends how easy it is to work with that 'plastic" piping. My new home has that sort of style of piping when it was remodeled, but I have no experience with it.
The installation of the heater complicates the build, but nothing ya can't overcome. Residential install standards can be a bit lax in some cities. The clearances are a bit tight for a gas water heater. You need to make sure your combustion air intake for the heater it not restricted or covered up and the stack and cap are not restricted in any way. You can get flame rollout when it first fired up if there are problems with either/both restricted.
Make some blocks out of plywood or make some "L" brackets so that you can take nuts and bolts or threaded stock and nuts to place underneath the plywood to tie the two halves together. I'd add some on top or where they join together at the sides.. If you want to add some more stability, add two pieces of plywood to the bottom with the same curvature as the outside diameter. Space them back enough you can put any sort of foam rubber so when you clamp it together, it exerts a force on the outside of the tank.
Make the tops as big as you can or want. It shouldn't be that difficult to make and is very "Hillbilly doable".
