i have already done the floor boards on my 81' with por-15. i am planning on puttin herc d.i.yurself liner over the por-15. i read an earlier post that said herc wont stick unless you put the "por 15" top coat. does the primer absolutley HAVE to be the por 15 brand? or can i use any primer of choice? please help, im doing to herc this week. thanx in advance.