That's something that can be discussed with the FEO when they call you to arrange the interview.Yes, no doubt you are right.
I would have thought it prudent to have a cabinet fitted however, and save yourself having to wait for a second visit.
Having said that Devon and Cornwall specifically say on their website "When applying for a shotgun or firearms certificate it is best to do nothing in relation to security until a Field Officer has paid you a visit."
Security - Devon and Cornwall Police Firearms
The security of the weapon is second only to the vetting of the applicant and British Standards gun cabinets (BS7558) are highly recommended.