I have used 18 hay bales running the 10m length of the tunnels. Irrigation supply was conveniently underground running between the two tunnels exactly in the right place to tee into it. I laid the bales long ways so the irrigation t-tape pipe could tuck under the bale the strings. I made sure to have the knots on the strings to the top to make it easier to remove them next year. I've completely soaked them all with the hose to begin the decomposition process. Going to try overwinter radish and onion in them.