Want to introduce myself

Hi Pro Handyman, would like to ask a question. I am a mildly experienced do-it-yourselfer and I am used to coming up with unconventional solutions to common household problems. I am stumped with this one; I have an idea but I don't know if it will work. Two years ago, my husband and I completely refurbished a single-wide trailer (due to financial circumstances from the economy, but that's a long story). It included an unplanned complete re-do of the entire bathroom. It turned out great except for the shower. We chose a middle-of-the-road shower kit made of high grade plastic. While the wall panels and shower pan themselves have held up nicely, we have one major problem. The manufacturer recommended ONLY silicone to seal the joints but there are several issues with that. Being a mobile home means that there is some 'give' and the silicone doesn't stick whatsoever to the plastic anyway so any wiping or cleaning causes the beads to come right off. Just the water hitting it causes it to come loose and subsequently it tends to grow mold around and behind the loose silicone (ick). My question is, do you think I could use some kind of semi-solid flexible grout to fill the joints that would remain sealed, stick to the plastic without eating it, and be cleanable and 'sanitizable'? Any ideas you have would be GREATLY appreciated!