Important things with the auto fuse mod:
Use 10a. Fuse. Here it is in the mod. Notice the word 10 facees up:
You bend the pos leg up and bend the neg leg down.
Here's a pic:
File paint off area where neg leg touches mod.
Place small piece of self stick rubber (like a piece cut from a glass tabletop cushion) between the positive contact and the part of the mod it could contact. Ensure that there is no chance that the pos leg could make contact with any part of the mod or it will not blow if shorted.
Place a similar piece of rubber beneath the pos side to level the fuse (since neg leg is bent down under fuse) and to provide some "spring" in the fuse when battery is inserted. Here's a pic:
Test the fuse by firing and shorting across the posts. It should blow instantly. This is a very important step. Don't forget the step. If it doesn't blow, the positive leg is making contact with something other than the battery. That is no good. The rubber pieces need to prevent positive from contacting any part of the mod.
I keep a spare up by the feed tube