G'day Fred,
I practise & develop loads from a portable bench I had made.
It's a bit cumbersome but it comes apart so I can get it into the back of my car. The legs screw into threaded plates that I bought from an irrigation supplier which are screwed to blocks that are glued to the bench top & cut at an angle a little so the legs are splayed ( to help with making it more solid).
It's a bit of a pain to get level out on farms but is achievable by scratching away at the dirt under one of the legs until it is balanced.
The idea of having one leg adjustable as per Pete's post is a very good one which I will have to think about for my bench.
It does wobble a tiny bit so I'll claim (tongue in cheek) that's it's good for technique......
Pic attached of bench & gear at a 300 meter range on a mates farm.
Take note of the target in front of a tree at 300 & go to my next post......
Regards,
Belly
Michael Bell