Strictly speaking, it doesn't actually matter if you haven't been to an airsoft skirmish yet, providing you manufacture a RIF with the intention of using it for airsoft in the near future, since the actual defence on that score says that you must prove that doing so was with the express intention of making it available for the purpose of that specific activity you are supposedly doing (or intend to do) and then claiming as a defence. If you think about one of the other recognised defences available, i.e. making a film or theatre prop, knocking up an orange plastic cap gun to look realistic by spraying it black, for use in your local am-dram production of Murder on the Orient Express or whatever, is manufacturing a RIF, and strictly speaking, it wouldn't actually be a prop until it either got delivered to the theatre, used in the rehearsal, or used the opening night of the play. We could equate that to making an airsoft RIF for use in skirmishes which has not been skirmished yet. However, I would tend to think that this line of thinking is doing a bit of a merry dance through the paragraphs of the VCR Act, and unless I had Atticus Finch (ooh, topical reference, ten points to me!) defending me, then I wouldn't wanna rely on that kind of nitpicking to keep me out of jail.
In practice, I would want something bit more ironcast myself if we were talking about the possibility of doing bird, so in my case I have a UKARA, I also work for a film production company where I use them as props for CGI, and I go to skirmishes regularly as well, so that's three bites at the cherry defence-wise, and all of them already in practice right now, which would I hope prevent a prosecution, but the aforementioned 'making it available for' is nevertheless what it says in the VCR Act. So whilst I think you'd be okay in regards to being pulled up by the CPS, personally, I would not be posting pics of knocking up a RIF on a forum for all to see if I was not fairly sure that a defence would be easy to prove if I were you, because me 'thinking you'll be okay', is no guarantee that you will be.
If you want the only jail you ever go to, to be the airsoft site at the former Ashwell Prison in Rutland, then I'd be a bit careful about what pictures you post.