Hi SteveH,
I know this is going to sound a bit Big headed but my bees do not propolise the touching edges of the brood box or supers. On saying that I do have one colony in Nat's that stick anything and everything down.
I think its about 2 inches thick the wall of the hives so to dig in with the hive tool is not too bad, remembering to go all round if possible. There is a knack to removing the roof and that is to press down on the centre of the roof and lift one corner, it comes off easy that way. I think they are all OMF mine are anyway.
A word of advice, check on whom is going to supply you with poly hives as some are not the right density of compressed polystyrene.
With today's prolific queens a National brood chamber is too small for them to lay in, therefor I always have my Nat's on double brood chambers.
With my Langs, if she need extra I use a super.
Regards;