I've done it on my 1140 AF. The panel to the left of the door to under the sink can be removed.
Pull the drawer above that panel to see inside and you should be able to deduce if there is enough room or not.
That panel is held in by staples.
I had to hammer (using a dead blow hammer) the front of the panel to push the staples out of the frame.
Of course that means placing a large wide block of plywood over the panel before hammering on it!
Using a pair of wire cutter (dikes) you can reach around behind the panel to pull the staples out.
Push the panel back to the front from behind if needed - that will leave the "heads" of the staple sticking up enough to grab them with dikes.
Later, you can reattach the panel with short screws and a specialty flat ratchet screw driver. (Remove all staples - be sure to remove any staples that pulled through the panel and remain in the frame.)
Hopefully, the 990 model is the same.
With the panel removed, you should be able to see the external power cord where it goes into a metal electrical junction box.
At that point, you should be able to fit the surge protector and improvise any mounting wood support for attaching the protector.
My apologies for not having photo'ed the install as I never thought anyone would attempt or need to do it!
2021 Arctic Fox 1150
'15 F350 6.7 diesel dually long bed
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