[DutchmenSport]

More than likely, cracks will continue, especially if you attempt to seal them up with something solid, like .... using a fiberglass (Bondo) repair on them.

What has happened is, the way the shower pan is anchored down did not permit any movement for the spots where it's anchored down (screwed down). As the floor of the trailer flexes, the shower pan does not. The pan is going to now crack at the weakest point (the cracks).

Now that is it's cracked, the cracking will slow down, but it will continue to crack out. There's nothing you can do about this as there is simply no room for movement where it's anchored.

Considering you don't want to replace it, your best option probably IS to simply tape up the cracks. This will allow the pan to continue to move and flex as you travel, but it may also spread or even create new cracks too. Still, not as much as it would you attempt to make the pan solid one piece again.

I think, your best bet, is to clean the shower pan very, very good, then use a rubberized spray liner on the bottom and cover the entire pan. In other words, you are creating a new liner on top of the old fiberglass bottom.

Creating a rubberized liner will seal up the cracks, and still allow the original cracks to flex.

Meanwhile, your tape may also be sufficient as it's basically doing the same thing. It just doesn't look very pretty.

I do know, once those pans crack and begin leaking, they only get worse. You own body weight standing on them will cause the cracks to spread, allowing water to pass under the pan and drip on down. A rubber liner will allow for the flexing. and keep the cracks sealed at the same time.