I have a bowed Cultured Marble Shower Base that I got from a garage sale its 36"x60" and very heavy the problem that I discovered it that in the center of the base where the drain is there is a upward bow it seems to be bowed enough for the water to move towards the 4 corners first then maybe head towards the drain is there a way to fix this problem or is this shower base a waste of time and a hopeless case ?
Thanks in advance

I've never heard of those things bowing, but if it is, I would guess that you could still install it, you just would be stuck with the water collecting around the sides. You could keep a squeegy in the shower to send it to the middle. Maybe over time and weight of people on it, it will flatten out again. The main concern is the drain opening itself, is it uniform enough around the edge for the drain.

I would set it down on a flat level surface outside and run some water in it to see what it does. Use a level to make sure it's level. Also when installing it on a mortar bed you could weigh the center down with a dry bag of mortar mix and check the slopes using a level.