First, did you have a look at this: [HOW-TO] SSHFS tutorial
You need to have your public/private keys setup properly. If so, something like this should work:
osmc@ip.of.server: /mnt/sshfsmount fuse.sshfs x-systemd.automount,noauto,rw,user,transform_symlinks,identityfile=/home/osmc/.ssh/id_rsa,allow_other,default_permissions,uid=1000,gid=1000 0 0
Try to manually mount it before rebooting for testing, but since noauto and autmount are used even if you get the entry in fstab wrong it won’t prevent your system from booting.