You could cut the job in half and just plant the seeds in the gutters. Works well at our place by the river .... well, until the dry spells hit, the grass withers and died, saves me mowing the gutters though .......
Mannum and the surrounding area gets a coating of top soil each evening in the dry spells and this builds a great garden bed in the gutters for the seeds to settle, sprout then die, a never ending job of gutter cleaning.
Thinking about putting bigger down pipes in the ends of each gutter length in place of the hole and down pipe under the gutters. Then, each time we have decent rain, the gutters will flush into the down pipe and all collect at the water tanks. I can build a floating material and sediment trap with the gap under the separator board to float off that stuff and the flow over the next board to remove the sediment, then on to the tank for the fine mud to settle, that will at least reduce the number of times the tanks need to be mud pumped and provide so more material for the compost tumbler ..... waste not want not
Then we have a good soil base for the new plants to thrive ....... until they die from neglect because they aren't self watering ......T1 Terry
A bit chilly though… 
maximum temperature should be about 11*.
Maybe adding an LPG tank in the interim before I get the hybrid electric set up installed and running, that's