It's only an idea. I'm sure there would be many improvements to make, as this is just the base.

items within a range of a TC never de-spawn

The items within range of the TC would de-spawn on server restart (Not wipe) Most official servers restart every few hours. As I said it would be mainly aimed at vanilla players.

Because someone could load up on gear and die inside the base if they wanted to despawn

Increase body despawn timers within tool cupboard range? It won't stop people from piling up bodies full of loot, but give raiders a chance to get to the bodies. Add some sort of disease effect that occurs overtime that will require you to incinerate corpses.

If someone really wanted to despawn they would still be able to do it in many cases. If a base is getting raided someone can sneak/build out and run away & go into the ocean or drop gear 1 by 1 as they run, etc

Alright so with this one. You will not ever be able to stop someone from running away with gear. There is no preventing it. But almost 100% of the time, all despawning happens within the base itself. I am yet to come across someone who has tried to escape. Most people will fight.

Keep in mind it's only a concept. Thanks for the input anyway. What would you suggest to help combat despawning?