Air can get past threads. I've had RTV sitting for months with one one on. It's the only thing I've been able to use that successfully keeps the RTV in the state where it can be re applied. I've tried plastic caps, I've tried shoving things in there, it always hardens. But yes, you need to keep the applicator tip on. I use an RTV caulking gun, so it stays on all the timeCaulk Caps, MARFOREVER Caulking Tube Caps 20 Pack Caulk Tube Sealer Cap, Caulk Saver Cover Sealer for Sealing and Preserving Open Caulking Tube
Good idea for caulk tubes with long smooth nozzles. If you left the application spout attached to an RTV tube and then used these, it would probably work short term, like if you were on a big project that required multiple application of RTV over a few days. But for long term storage, I don't think anything could beat Frank's suggestion of tapping the tube opening and installing a screw.
The hybrid pan is nice, I'm running one. Just know there's a bit of modification you need to do to the pan, and likely a small amount of filing on the backside of the condenser body where the threads for the mount are.Have a hybrid pan coming from cascade as well as radiator support ac compressor, dogbone, condensor , radiator coming from fcp euro. New subframe with poly bushings coming as well. Control arms and ball joints and tie rod ends were all replaced 60-70k hwy miles ago so will skip that.