Fwiw...BRe...
Imo, 3 keel bands are essential, as GW says above. Also consider that (like the wood rubbing strakes) they are relatively easily fitted at build, but much harder later.
Also surprised that these keel bands are now "extras". Sign of the times? I believe the wood rubbing strakes always were?
Rain and Sun covers are not cheap, but they are good quality and have proved to be durable on both my BRe (4 years for my mast up mooring cover - has this year required the bungies replaced, otherwise aok) and also on two racing dinghies. All left outside, all summer)
Mine is a grey PVC type material ("coolmax" or similar material?), the idea being that its more durable, and easier to clean than the buff canvas of my other canvas items.
Recommended.
I think the yard may hold stock, hence makers directing you to yard?