Jim - in response to your PM here are some pictures from when I was bonding the body that show the heater hose holes in the fiberglass firewall and aluminum skin.
The two holes just below the main electrical cable entrance are for the heater. I believe the three screw holes around it are the one to secure the heater - one to either side and one below. Assuming ERA supplied the same heater to you as they did in my kit, they should be the same on the template.
This is of the firewall behind the aluminum. The lower heater support screw is below the steel tube cross bar and only penetrates aluminum. The threaded coupler allows adjustment to make up for the thinner section in that area.
Here is another picture of the interior with the heater mounted. I took hundreds of photos but still managed to miss a lot of good detail shots I could have taken.
Hope this helps.