Make sure you only do it once by getting the preparation right.
Prepare the area well by digging out any weeds and big stones then levelling the soil as flat as you can and firming it down. Spread on a layer of weed suppressant membrane and peg it down. Put a border round to conatin the bark chippings so they don't spill out onto neighbouring beds or lawn. You can use bricks, stones, log roll, rope tiles or whatever suits your taste and budget. Fill with bark to at least 2" deep. More if you can.
The bigger grades of bark will rot down more slowly than the finer stuff and are les slikely to blow around in strong winds. You'll still find some opportunist weeds will seed into it but they're easy to clear.
Install your seat and enjoy.