There's nothing in the rules, how big the grass area on each field has to be to place the barn. And footnote 180 in S-CAR 7.4 states, the barn can be placed on a volcano tile, while the volcanoes on the CFFF and CCFF tiles are also quite close to at least one of the meadows corners. Also consider footnote 298 for bridges <-> tower interplay, where it is stated, that they don't interfere, because the tower pieces can be deployed next to the foundation as well. So I think it is a safe bet, that there is no issue with barns either.