Those GRIF form bases look really cool! I like our Corian counters in the kitchen, I think Corian would be an excellent choice for a shower base. We installed a Swanstone base in our shower about 3 years ago. It has been very easy to maintain, but I guess I can't speak to long-term durability. The shower is used every day, currently by 4 people while we remodel the other bathroom. I'd say it still looks as nice, today, as it did when we installed it. I like the raised non-slips more than etched (our new Kohler Villager cast iron tub in the other bathroom has etched nonslips and they feel like chalkboard to me -- I'll probably stick the bathtub mat over them when the remodel is done). I'd go with Swanstone again if I had to make the choice. We also have the Swanstone solid surface shower niche, and that is a piece of cake to maintain.

You probably have made your decision by now. I recently had a horrible experience with customshowerbases.com. Their custom service was excellent until we fully paid for the order. Everything went downhill from that point. (1) Promised two weeks manufacturing, but it took FIVE weeks to get to us. No one updated us any of the delay in the meantime, until I called. I am pregnant and due in a couple of weeks, such delays are not acceptable! (2) Arrived product is flawed with extremely low flange height than indicated on their website and even lower than indicated on our custom drawing. This is a big deal, as any flange height lower than the threshold will cause water leak....they are supposed to be experts in this realm, oh well… (3) Base outside dimension is off by 1/4", more than their promised 1/8" tolerance. This is also a deal breaker, as this creates larger gaps around the base and our existing tile floor! (4) Arrived with minor chips on the corner, which is not a big deal. With all the issues, they refused to send me a new one. If anyone is considering this company for any of their products, you know what to do....

We have a 75” x 40” garden tub we want to remove and replace with a large shower in that space. What solid surface materials are available other than granite or marble? Are there shower ’kits’ avialable in custom sizes?

I have always really liked corian in light solid colors - whote, cream etc. Looks timeless for a more modern or contemporary kitchen. Compared with patterned counters, that are often a dating factor (think brown granites of the tuscan era and white/grey veining of the current era). Separately, my parents did an all white semi traditional kitchen in 1989 and used white corian. They updated the hardware, appliances and backsplash when they sold 30 years later, and the kitchen ”sold” the house. High end suburb, fwiw. This goes back to the point I often make on this forum, which is that if you’re specifically asking about resale choices, buyers only care where things look updated and/or neutral, even if the quality of materials is what this forum thinks of as low end (think lvp).