How to make a Rust no-decay plugin (per-category multipliers)

using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using Oxide.Core;
using UnityEngine;

namespace Oxide.Plugins
{
    [Info("No Decay", "RustPluginGenerator", "1.0.0")]
    [Description("Cancels or scales decay damage per building grade, deployable and vehicle.")]
    public class NoDecay : RustPlugin
    {
        private const string PermInfo = "nodecay.info";

        private PluginConfig config;

        private class PluginConfig
        {
            [JsonProperty("Twig multiplier")]
            public float Twig { get; set; } = 1f;

            [JsonProperty("Wood multiplier")]
            public float Wood { get; set; } = 1f;

            [JsonProperty("Stone multiplier")]
            public float Stone { get; set; } = 0.5f;

            [JsonProperty("Metal multiplier")]
            public float Metal { get; set; } = 0f;

            [JsonProperty("Top tier multiplier")]
            public float TopTier { get; set; } = 0f;

            [JsonProperty("Deployable multiplier")]
            public float Deployable { get; set; } = 0.5f;

            [JsonProperty("Vehicle multiplier")]
            public float Vehicle { get; set; } = 0f;
        }

        protected override void LoadDefaultConfig() => config = new PluginConfig();

        protected override void LoadConfig()
        {
            base.LoadConfig();
            try
            {
                config = Config.ReadObject<PluginConfig>();
                if (config == null) throw new Exception();
            }
            catch
            {
                PrintWarning("Configuration file is invalid, using defaults");
                LoadDefaultConfig();
            }
            SaveConfig();
        }

        protected override void SaveConfig() => Config.WriteObject(config);

        protected override void LoadDefaultMessages()
        {
            lang.RegisterMessages(new Dictionary<string, string>
            {
                ["Info"] = "Decay multipliers: twig {0}, wood {1}, stone {2}, metal {3}, top tier {4}, deployable {5}, vehicle {6}",
                ["NoPermission"] = "You do not have permission to use this command."
            }, this);
        }

        private string Msg(string key, string userId = null, params object[] args) =>
            string.Format(lang.GetMessage(key, this, userId), args);

        private void Init()
        {
            permission.RegisterPermission(PermInfo, this);
        }

        private void OnServerInitialized()
        {
            Puts($"NoDecay active. Multipliers: twig={config.Twig}, wood={config.Wood}, stone={config.Stone}, metal={config.Metal}, top={config.TopTier}, deployable={config.Deployable}, vehicle={config.Vehicle}");
        }

        private object OnEntityTakeDamage(BaseCombatEntity entity, HitInfo hitInfo)
        {
            if (entity == null || hitInfo == null) return null;
            if (hitInfo.damageTypes == null) return null;
            if (hitInfo.damageTypes.GetMajorityDamageType() != Rust.DamageType.Decay) return null;

            float multiplier = GetMultiplier(entity);

            if (multiplier <= 0f)
            {
                hitInfo.damageTypes.ScaleAll(0f);
                return true;
            }

            if (multiplier != 1f)
            {
                hitInfo.damageTypes.ScaleAll(multiplier);
            }

            return null;
        }

        private float GetMultiplier(BaseCombatEntity entity)
        {
            BuildingBlock block = entity as BuildingBlock;
            if (block != null)
            {
                switch (block.grade)
                {
                    case BuildingGrade.Enum.Twigs: return config.Twig;
                    case BuildingGrade.Enum.Wood: return config.Wood;
                    case BuildingGrade.Enum.Stone: return config.Stone;
                    case BuildingGrade.Enum.Metal: return config.Metal;
                    case BuildingGrade.Enum.TopTier: return config.TopTier;
                    default: return 1f;
                }
            }

            if (entity is BaseVehicle || entity is BaseHelicopter || entity is ModularCar || entity is BaseBoat)
            {
                return config.Vehicle;
            }

            return config.Deployable;
        }

        [ChatCommand("nodecay")]
        private void CmdNoDecay(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermInfo))
            {
                player.ChatMessage(Msg("NoPermission", player.UserIDString));
                return;
            }

            player.ChatMessage(Msg("Info", player.UserIDString,
                config.Twig, config.Wood, config.Stone, config.Metal, config.TopTier, config.Deployable, config.Vehicle));
        }
    }
}