2001 4Door Prerunner Behind Seat Subwoofer Install (HELP ME!)

So, I've seen a lot of forums on this website about doing a behind the seat install of 2 8 Inch subwoofers with a custom box made by Supercrewsound.com , as I was very urged to jump at this idea I decided to pour my financial assets into this idea without knowing much of what I was doing. So I went to purchasing two 8''s on eBay both JBL Stage 810 Subwoofers that I was told by supercrewsound (very helpful customer service by the way) that would fit in the custom box made by them. These arrive, very pleased with the quality, I order the box. Now the box has arrived and I have jumped into trying the speakers with this box. However I am blessed with this (See Picture Below)
The absolute fear that I was hoping wouldn't happen! Supercrewsound had told me the mounting depth was 4 inches on the box however the mounting depth was when measured very precisely 3.865inches. The speaker seems to however fit in the box but from one side too another when moving around.

Can anybody find a fix to this???????????? Is there an adapter or a rubber piece or something I could to get this mounted correctly or properly?




Now just as you are most likely thinking it couldn't get any worse I'm at a loss at how this box is supposed to fit behind the seats as there is a very nifty place where the metal is shaped behind the passenger side back seat that's not allowing me to get around this so I may place the box behind the seat. (see picture below)
What am I supposed to do about this? I've seen people place boxes back here all over this forum so I know it's possible. It looks like its welded on. Do people cut this off? If so how? And what should I do to get around this?





If you're curious about what the box looks like this is it:





If anybody knows how I can get around these obstacles that'd be great! I do know it's possible as I've seen somebody even place as many as FOUR 8's back there! I can't even imagine how that was done as I can't even get 2 8''s to fit!