Yes, with a little effort it is quite possible. We recommend setting the posts in concrete in addition to a plastic tube, which you can later remove from the concrete foundation.
You should then follow these steps:
1. You get a HT or KG plastic waste water pipe with a diameter of 150 mm from a hardware store. You should get a piece of 60cm length per post or cut it off to fit.
2. Now dig out the foundations according to the assembly instructions to a depth of 30x30x60cm (alternatively drill with an earth auger) and insert the post into the plastic tube and into the foundation hole.
3. Now mix the mixture for the concrete foundation (available in sacks as a ready-mix at hardware stores) and fill it in between the post and the pipe as well as between the pipe and the ground.
Then tamp it down well with a short wooden slat or similar so that no holes or cavities can form in the concrete.
Advantage of this approach: You can later dig up the post foundation and use a thick hammer and chisel to knock the outer concrete foundation off the HT pipe. The post, including the inner foundation and HT tube, can then be concreted in again at a new location.
