We purchased a 15 yr old mfd. home. Master bath has an ABS(?) bathtub with separate shower walls. It's serviceable, but will eventually need to be replaced(ugly). A: I would like an all in one insert tub with walls. I can see, without measuring, the walls are not square. Is an insert possible without a lot of finagling? We're on a limited budget. B:If I cannot do an all in one insert, what r my best options for material for the tub and the separate walls. The shower walls right now are board with vinyl over them, doomed to fail. Again, not looking for Top of the line, something economical, easy, sturdy, easy to clean. Thanks.
I have replaced dozens of older tub/shower units with nice fiberglass tubs with a three piece matching/interlocking surround wall kits. Since getting a one piece unit into old construction is usually impossible, these modular units work well. The better units are sturdy and will adapt well in situations where the walls are not perfect. Since the wall units interlock and overlap the tub flange, leaking is rarely a problem. The costs of these units run from about $500 to $800. I have good results with Kohler and American Standard units. Avoid the cheap units that have non-locking wall sides and require a lot of sealants and flimsy corner trims. This is not an easy DIY project for someone without experience. The process will include plumbing skills, leveling the tub unit and shimming the walls if the existing wall framing is really bad. Sometimes it is necessary to remove existing wall sheathing (drywall etc) and attach tub and sides to studs, then use moisture/mold resist drywall to recover the walls.
As Shirlock & Grunthos say, you're probably not going to be able to do a one-peice (unless you cut a large hole in the wall.) I did a tub and surround a few years back, tried a budget plastic surround, got it home, pulled it out of the box, put it back in the box, returned it and upgraded to a (3 peice) fiberglass surround that cost a bit more than the new tub - the cheap was was clearly too thin to actually last (or possibly even survive the install.) This was a limited project to get the house sold. I figured I would not want to buy a house with the cheap plastic surround, so who else would? Might as well leave the rusty leaking steel tub I was replacing in as use that piece of junk.
To make the most of DIY in a project where it's not just to make the bath look good enough to sell the house, I'd consider tiling it rather than even a "good" fiberglass surround. More DIY mileage and a nicer end product - potentially at less cost. If that sounds scary, try a few smaller tiling projects first - it's less daunting when you have done some (or you'll find out it's not your idea of a fun time on a smaller project.)
If you use a fiberglass (or other plastic) tub, bed the thing in plaster - it should be in the instructions, if not, well, find some elsewhere. It makes a world of difference in how the tub feels and holds up over time. Literally as simple as placing a pile of plaster on the floor, and then setting the tub, so the plaster fills the space between the tub bottom and the floor, fully supporting it. Nothing wrong with a fiberglass tub if you attend to that detail and don't scratch it up - cast iron is "more solid" out of the box, but also expensive and heavy - the only end benefit (to an annoying install experience dealing with the heavy thing) is that you have a harder porcelain finish.
I personally won't use even "moisture resistant" drywall around a tub. Tile backer (durock, hardi-backer - stuff comes in 3x5 sheets, normally) is far more moisture resistant and does not cost a lot more for the small area - so if anyone ever decided they don't like the fiberglass surround in the house we sold, they'll find tile backer behind it. There's also framing to support grab bars if ever needed.