Every way to raid a faction base minecraft?

Have you attempted to use sticky pistons? This really only works if their structure is right on the border of their land but you can use them to extend into their land and remove a block so that you can enter and use enderpearls etc from there. You can also try using water next to the faction land that flows into it so you can scale walls etc and also you can try burning nearby trees to see if you can get the fire to spread into their land.