Use one or the other - there's no configuration that will give you optimal results by combining them. The liquid product will give you somewhat better panel stiffening than the mat, but can't be removed. Things like simple door dings become very difficult to repair. Either product needs to be in direct contact with the sheet metal to work well. If you put the liquid on top of the mat, all it will do is reinforce the constraining layer of the mat - the softer butyl layer on the mat will compromise the liquid's stiffening performance. Putting mat on top of liquid will be 100% wasted. The mat won't be in direct contact with the sheet metal and the porous surface of the liquid provides a poor surface for adhesion.