Reddit reviews Whirlpool W10113902A 30" Gap Filler Kit
We found 2 Reddit comments about Whirlpool W10113902A 30" Gap Filler Kit. Here are the top ones, ranked by their Reddit score.
Whirlpool (WHIRA)Genuine Replacement PartOven-accessories
https://www.amazon.com/gp/aw/d/B00L4I780W/ref=mp_s_a_1_1?ie=UTF8&qid=1482619003&sr=8-1&pi=SX200_QL40&keywords=Whirlpool+side+in+range+filler+kit&dpPl=1&dpID=21DIdoanhKL&ref=plSrch@
Try this. It doesn't mount to the range but this is what is meant to fill that gap on their more recent slide in ranges. Should work for what you are describing.
Having the same dilemma here, might end up using something like this and caulking it with silicone. It's a gap filler for behind slide-in ranges, they're 30" wide already.
https://www.amazon.com/Whirlpool-W10113902A-Gap-Filler-Kit/dp/B00L4I780W