Seed Saving Leeks

Every year I try to save more and more seed of different varieties for veg.

This is for a few different reasons.

Isolation Cage?

This is nothing to do with the current problems facing the world. But all to do with seed saving. 

I have ten of these lovely looking board beans that I want to grow this year called Gloster Bounty. Trouble is it's not enough to eat a good meal of (when grown) and I know it likes to cross.

Ideally i'd like to build my stock of this seed up and grow it properly next year. So to do that I'm thinking about building them an isolation cage over the top. I'm not sure how well they'll pollinate then though, will I have to do it by hand or introduce pollinators like flies from fishing maggots? I'll need to do some research before that time comes! I love the idea of building my seed numbers like this! Hopefully I'll get enough to grow out a full bed next year!

Anyone else grown plants in an isolation cage and had to introduce pollinators?