How many times you changed your mind about the weapons options of a vehicle? It happens to me every time I'm trying a new army list! Since I don't want to buy a new vehicle just because I changed my mind on his weapons I usually make all the weapons removable, this is my trick:
I drill some holes using my Dremmel on the weapon slot and then put some small magnets into the holes, I put some superglue on them after I'm satisfied with the result
I glue some flat magnets on the weapon attachment
And this is the final result, if you change your mind you can build another weapon option just buying some bits (check http://www.bitsandkits.co.uk/)