Your way sounds good too. As well as tape the ends closed. John
I have used the rubber caps that come from an acetylene torch. I went by the local dealer just before last X-mas and he gave me a set of 4.
Bob
Years ago Cat had aluminun threaded caps to put on the pumps & nozzle & later years they came with plastic caps on them. Any way to cover them is good so no dirt gets in them.I always had a bunch of the threaded caps so was no trouble around the shop.The real early caps I saw too were brass nuts (caps).
Small balloons work great, and are cheap!!