Water Leak in 2010 F150

I just discovered a major water leak on the passenger side of the vehicle. The rubber floor liners hid most of the symptoms and prevented me from catching it earlier. When I found it this weekend the wire well running the entire length of the truck was full of water and the underlayment pad between the carpet and the firewall is toast. To add insult to injury there were a ton of fire ants underneath the soaked pad.

Apparently the most common cause of the leak is the gasket on the middle tail light above the sliding glass window. I confirmed this is likely the source this am when another storm passed through.

Anybody dealt with this before or have any recommendations on a shop I should bring it to that will fix it right? I called the body shop that has done most of my collision work in the past but they said they only deal with collisions. I talked to another mechanic that comes highly recommended by a couple of people but he has work scheduled 3 weeks out. He did say because of the fact it is water and needs to be handled ASAP he could squeeze me in but it will likely take a week to diagnose and do the work.

He said my best option is to pull the front passenger seat and as much carpet as possible to start it drying now to save time once he receives it.

If I am pulling the seats, carpet and know the ingress point is obviously the gasket on the light how difficult would it be to do myself?