I'd rather you than me. Bath really needs taking out and fitting properly, but that's probably not an option. If the bath moves a lot, you might be better off with duct tape until you can stop it moving as anything else will not last long enough to be worth the hassle.
I don't like using strip. Sometimes you have to to cover an ugly gap, but it would be better to seal behind the strip with silicone so you aren't relying on the strip to make the seal. Strip often doesn't seal effectively and fails to stay in position. If you try this one with success, do let us know!
I wonder if you can get behind the bath (perhaps from below) and form a backing to cover the gap with expanding foam or what have you and then you have something to pack the silicone against. Or just use silicone in between as best you can and also surface mount it to form a kind of miniature scotia moulding over the front edge of the tiles. It won't be the neatest bath edge on the planet, but can be made reasonably presentable (use masking tape to get a clean edge if you haven't much experience with silicone).