Traveller: Bootwell floor / inside corner of woodwork gap

[GheeBhow]

Hi all,

I'd be grateful for a bit of advice please. I'm part way through replacing the bootwell floor of my Traveller (and inevitably, part of the inner wing too), and there are finger-wide gaps between the left and right edges of the bootwell floor / ends of the flanges and the inside corners of the corner posts (which are original).

I think that's fine, and the original bootwell floor was like that - but what's the best material to use to fill the gap? I'm assuming that it should be filled to stop water getting to the coach bolts and so on. It would take quite a lot of Dum Dum, but that's one option. But is it the best choice?

Thanks for any views,
Neil