I'm not familiar with fiberglass bathtub problems, but we had a fiberglass shower that developed a hole where it was unsupported below. My coworker put a bag of sand (no hard edges and it would sit there nicely) underneath the hole for support, and then he sanded down an area around the split, resurfaced the small area, and painted it good as new. Essentially, that is how they repair boat hulls too, when they get defects in them. I would say you do not need to remove the tub, most of the time fiberglass repair is a quickly done job. (Think about those lovely Corvettes having fender benders and getting fixed good as new.) Can you contact the tub manufacturer? It might be they will tell you who to call in to make repairs. Or, like the above poster indicated, you could go for a long time with no leaks and continue to use your tub.

There is normaly an opening through the slab called "leave out" beneath tubs that will allow routeing the drain as will be needed. If there is no leave out when you remove the tub,just raise the floor of shower above slab enough for drain to go underneath. Retro-fit all in one showers normaly sit high enough to use a "shoe"drain to address this. You didn't ask but before you get too far along, I reccomend measureing your doors and halls to make certain you can get the shower into the bath room.

I respectfully disagree with Jon Boy's recommendations to put decals on your tub. You will be permanently defacing your tub with those decals. Try ever getting them off. It's impossible to do it; there'll always be residue and the shadows of those decals. You will also have the same problem as with a non-slip surface--those decals with their textured surface (as described in Jon Boy's link), will grab onto grime and keep it. I also disagree that using a bath mat is like "your grandma's house or a cheap motel". If you need a bath mat, use it, for goodness sakes. Roll it up and put in in the cabinet or vanity when you are done with it. Besides, perhaps the OP is a grandfather, and Jon Boy inferring that being at a grandparent's house is something negative to avoid is condescending. One of the tubs in my house does not have a non-slip surface, but one of my other tubs does. The one with the non-slip surface (it's cast iron) is permanently dirty looking, despite all my efforts to clean it. For the tub without the non-slip bottom, I personally have never found the need for a bathmat, but I do keep one on hand for guests who might want one. It's nice to have that flexibility. Decals are permanent, and kinda '80's too.

Thanks for the suggestions. I had not heard of Abitibi board before. I goodled it but seems like abitibi makes so many different panels so I did not find anything specific for bethroom enclosures. I assume the abitibi panel sombreuil_mongrel is talking about is a waterproof type of panel? Seems like an attractive option if I can find it in the San Jose,CA area and if they make enough trim/flashings to achieve water tightness around the window. Mooie, thanks for sharing your tile experience. I may consider tile too, after all. I even thought of perhaps making something from scratch myself around the window like fiberglass (liquid form+glass cloth) or same with epoxy and glass cloth? On the other hand, IÂm weary of using non standard methods/materials in case I ever want to sell the house. Unfortunately I have found that inspectors tend to flag anything they are unfamiliar with even if it is superior to the "standard" stuff.