Here is a pic of my electronics that just fit under my cafe seat.
As far as making a hoop, I used the stock grab bar, cut it into a arch and weld it together. It is very stout and will be more than I will ever need as far as strength. If you have the grab bar, cut it in half and then turn the curves to make a better arch, some detail work to get it to be a smooth radius, but it worked great.
My suggestion is to first figure out what seat hump you want, as this will determine the length of hoop you will need, then firgure out what electronics and battery you will want. All of these need to fit together, and if you don't have space with the seat choice, you may have to rethink things. I think going to modern electronics is not only smart and a good investment, but gives you more space when things get tight under the hump.
There are many posts about almost any part of the building a cafe, just think ahead before you go cutting and welding.
Hope it helps!
