From my own experience from stamping mnemonic recovery words into washers I find it crucial to have a sturdy, solid, heavy and non-flexing base where the washers are placed on. So I wouldn't recommend to avoid using an anvil or some big enough solid block of scrap metal with some suitable flat surface(s). The heavier, the better...
I totally agree.
While stamping, a big part of the process is keeping everything in the right place. I bought a small anvil, and I think it was enough. But of course, a bigger one would have done no harm.
The base, apart from being metal reinforced is made of solid PLA+ or ABS, and it withstands the hammer impact quite well. The washers are grabbed tightly and fixed, which facilitates the process a lot.
The jig I used was basically without any base, and I fixed the washer with simple scotch to the jig base. I have a sense that having a base would cause irreparable damage to the bottom of the jig.
Do you reckon the is not the case and that the whole jig is sturdy enough to sustain such mechanical stress?