Did this myself a few years ago. Plumber fitted the bath etc. but I was tiling the bathroom myself. I actually used two trims (to be sure!) and the sealant. I put one trim behind the tiles (directly onto the wall) and flush with the bath - I used the sealant to stick it. Then I tiled the wall and put another trim over the tiles - again using the sealant to stick it. Probably went a bit overboard alright but it was a bedroom we were converting to a bathroom so didn't want any sign of a leak - better to do it properly first than having the hassle of fixing any leak damage! It worked fine and never had any leaks. In your case pbyrne I would use the trim and the sealant.