the KC-110 from Roland is convenient, that's right.
But it has to be put on the ground. Which is not very well when the ground isn't flat or clean.
The solution: the KC-110 Amp Stand. Plus, it comes with a travel bag. In this bag you can, of course, put the amp stand but you can also put the theremin stand with it!
So one hand for the theremin, the second hand for the amp, the back for the battery and the stand bag.