Please, add an option to lock a fuel tank and storage (if there is one) of vehicles similar to mounting using same logic. At this moment, while random players can't be mounted if this protection enabled, they still are able to loot fuel/storage.

I would encourage us to evaluate whether this plugin should keep adding features. This plugin already has an excessive amount of features and options, making it hard for people to even determine whether it will work for their use cases, let alone configure it.

Locking vehicles is useful as a standalone plugin. Implementing it here too just increases the overall maintenance burden for the uMod developer community to maintain the same functionality in multiple plugins, and makes it harder for the next maintainer of this plugin. If it's very useful to players to have the option in this in this plugin, then I suggest the feature be added via integration with another plugin (which may need to be created).

This suggestion is about vehicles bought/spawned by player using this plugin only. I'm not talking about locking of any other vehicles.
This plugin already have a player mount protection system wich prevents "random player" to be mounted on a driver seat, or even any seat. IMHO it's logical to have the whole vehicle protected. Pretty strange to have "private vehicle" that costs some ingame surrency and any random player can stole fuel from...
I'm only talking about functionality, not architecture. It seems not that convenient for me to have another plugin to install, but I will with no problems, if I have to.

I understand there's an already a locking feature in this plugin and that it's incomplete. My post is more of a general callout to make sure we are thinking about these sorts of things instead of blindly adding features which authors seem to do often.

I agree it's not convenient to install another plugin, but it's not a lot of effort if designed well (i.e., only install the file, no config required), so it's usually more of a psychological barrier than a physical one. Developer time is by far the most scarce resource. Though not immediately obvious, optimizing for convenience in the short term can actually result in reduced developer productivity in the long term which can be worse for consumers. It's also not convenient for consumers who just want locking functionality to have to install a large complex plugin to get it, or to be unable to get it because there isn't a standalone plugin.