Tried my luck at this again this weekend... This time, new steel to mess with (without holes first, as that seemed to be my initial problem) and a little more patience.

I guess it paid off... I got the brackets cut, drilled, and mounted. The one on the left side (while sitting on the bike) seems to be touching the frame though and there is no way to get a bolt in through it unless you'd raise the box. However, it seems that the bolts that I've got in now would hold it in place just fine.

My only problem at this point is... the filter STILL won't fit! I bought one of those from the site here. Maybe if I would've put the filter on first, and then put the battery box/battery in afterwards it would've fit right... But if I have to maintenance anything there... A huge pain?

I'm thinking of doing what I was thinking of before... And just going the route of a custom box of some sort.