If you attract the wrong type of attention with deacts, irrespective of if you are carrying the certificates, the Police will seize your weapons as they will say only firearms trained personel can make the decision on whether they are actually compliant. You can then have a very long wait and a lot of hassle trying to get them back.
I have seen modern SAS type landrovers with everything fitted and covers on the MG's, but is it realy worth the risk and potenial hassle. Providing you have the necessary excemptions to be in the pocession of replias its not so much of a problem, but the police will still stopped you if they don't like what they see or they think you are distracting other drivers.
How you store them at home is down to you.