My tub drain was cocked, warping the tub floor at the drain when it was built. There was always a puddle of water that would not drain from the tub. The drain piping under the tub was installed incorrectly causing pressure on the tub drain fitting making it warp the tub floor.
The dealer did an improper warranty fix by cutting away the piece of wood paneling on the side of the tub and adding a pipe strap to pull the drain straighter. He then restapled and glued the paneling back to the wood framing supporting the tub.
It was better but water still puddled in the tub. They also put the piece of paneling back but there was no support at the edge where they cut it to remove it. You could actually push it in and stick your fingers under the tub.
I removed the paneling again and replaced the fittings under the tub with the correct length pieces so that the drain would not warp the tub. I had to remove the tub drain and reseal it because it was pushed out of alignment with the hole in the tub and I was afraid the pushing back-and-forth to get it straight again would cause it to leak.
There was an access panel that could be removed in the bottom of the closet that allowed access to the back of the electrical panel under the closet door, access to the drain plumbing for the tub and connections to the grey water and black water tank vent pipes.
I could only reach the drain piping with my right hand. I was able to get a neighbor to help hold the drain in place and keep it from spinning by using a pair of needle nose pliers while I tightened the drain fitting nut and again when I tightened the p-trap to the drain fitting. I also used fresh plumbers putty on the drain fitting.
I reinstalled the piece of paneling on the side of the tub by adding a piece of 2x2 to support the edge of the paneling and reattached the paneling using painted screws to keep it removable in case I had to go back in. Every once in a while I would check in through the bottom of the closet to make sure the drain piping wasn't leaking.