Graeme
On my recent models, the figures, if they are not small scale, have a 1<1.5mm dia. brass peg out of the bottom of a foot, which goes through the deck, which if planked will be on the caulking, and the figure is then held with a spring and collet underneath the deck, so no glue is needed and the hole is within the black caulking if the figure ever has to be removed permanently.
Alternatively, put the figure on a suitable grating, perhaps by a gangway, or behind the steering wheel, or in front of a doorway – the 'hole' will be easily lost in the grating's spaces and the deck underneath is not damaged by glue.
The advantage of 'spring-loading' a figure is that it moves when one, as is inevitable, brushes a hand against it when fiddling around inside the model as I have frequently discovered.
Paul Freshney