I always mount my fuses right off the battery. You can bolt it down or zip-tie it there.
Install looks great! I have never seen subs mounted this way...usually I mount them firing to the rear and down, but it does look really cool. In the past I have found this fan
to work very well in applications similar to yours. It's more expensive than a PC fan, but I have noticed that it cools it much better (and it can be hidden, so it looks better IMO). Add some plastic spacers under the amp to raise it off the carpet for ultimate cooling.