Dual Subwoofers: close together?


I’m getting two subwoofers for my new home theater, and am in a dilemma as to where to place them.

I know opposing corners is an optimal placement, and indeed this is possible in my situation. In those two corners, the subwoofer would be uniquely unsightly.

Placing the to either side (outside) of my left and right channel towers is NOT possible.

What is possible is to have them on either side (inside) of towers. So the order is:

left channel -- subwoofer 1 -- center -- subwoofer 2 -- right channel
(Please see attached photo). https://pasteboard.co/HGb3bQL.jpg

The problem is there’s not much room, and everything’s fairly squeezed. Also, the subwoofers would be placed inside a built-in wall cabinet (the front would be covered by a fabric, the sides and top plywood, and the back a wall).

I know this arrange will be far from ideal, but my question is how much of an impact should I expect compared to placing it in the ideal opposing corners setup? Is it a problem having the two subwoofers (1) so closer together and (2) placed into an enclosure?
xdc
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The benefit of multiple subs is the ability to equalize the bass energy in the room thus eliminating or smoothing out nulls and peaks. Experiment with placement is the key as no two rooms are the same.  You can also invest in an inexpensive SPL meter and test record/CD to help measure bass response in different sub placements. 
@brf is right

But if you can afford a HT system and dual subs, splurge a little and get something like OmniMic. :)

There’s a secret though. Put the sub in your listening location, then move the mic around to try to find the best sounding speaker location you will accept. Once you have it, play the first sub, and move the mic around to the second best possible location until you find the worst sounding place. This will put the sub in a complementary position to the first.

Bass traps really help in giving you more placement options, and EQ's are usually still needed. 

Best,

E
I placed my two SVS SB2000 subs just inside my main floor standers and to either side of my equipment rack and this works very well. They are separated by about 6 feet. Lenrd bass traps by Aurelex in the corners of the room stacked three high help tightness and clarity of bass response.
I have 4 JL Fathom F-113's. 
2 are located behind the front speakers and the other 2 are spread out behind my listening position. 

To me, the more subwoofers used, the more there locations disappears.

ozzy