I assume you are just wanting to remove a 14”-18” path through the rear sun pad and put down a non slip finish like Seadeck, then redo the edges of the upholstery. If that’s the case, an upholstery shop is your best bet. Removing the pad is not a big deal. It should be held on with nuts on the backside.
Of course, you could do what most do and just walk over the padding. Then, if in five years you’ve damaged it, do the work at that time and just have the same shop charge about the same price. You’ll also know if you want the walk on the side or center. You might prefer keeping the pad.
If you want to change any fibreglass to make a real walk through, just follow Scott’s advice.
