You can use these commands to create/remove invisible walls and spawn barricades on them and kill the barricades later.
*setwall "<map name>",<x>,<y>,<size>,<dir>,<shootable>,"<name>";
*delwall "<name>";
Creates an invisible wall, an array of "setcell" starting from x,y and doing a
line of the given size in the given direction. The difference with setcell is
this one update client part too to avoid the glitch problem. Directions are the
same as NPC sprite facing directions: 0=north, 1=northwest, 2=west, etc.
Then you can use
areamobuseskill "<map name>",<x>,<y>,<range>,1905,"NPC_INVINCIBLE",1,0,0,0,0;
This is not the best practice for making barricades invincible. But who cares? Players can't pass the wall if the MVP is alive and killing the barricades is going to take them long time that they will get killed by the MVP first.