The first thing I did when I got this model was to look and fix any loose glue joints and supports. Like with any ARF these days I did find a few places in the forward section of the Fuse but they were minor. I do recommend reinforcing the firewall and the main gear block with 2 hour epoxy.
The manual shows detailed photos of the critical areas to support and glue.
After the glue was setup It was time to seal the firewall and epoxy it to help rein force it and to seal it from gas and or glow fuel. For a plane this big gas just makes the best solution.
1.I used balsawood to seal the center hole of the firewall and reinforce it as shown in the photo using triangular stock.

2. 2 hour epoxy should be used to seal and further harden the firewall. A few drops of lacer based paint mixed with the epoxy can be used to color the area to your liking.
3. Then I centered the firewall after it had had time to completely dry.
4. I use this center point to lineup and center the engine mounting plate to the firewall.
5. I marked and drilled the holes for the mounting hardware and fit the spacers and vibration dampeners. (as recommended by engine manufacture.)
6. I mounted the engine as shown taking care not to over tighten the mounting hardware. Here are how things looked step by step.