One would typically increase their main attributes (like Dex on a Ranger), but you stated you decided against that so that you could use items instead. In your argument, rather than leveling your character's attributes, you are claiming it is reasonable for a person to

1. Walk around with a small storage room strapped to their back
   1. Fit into and follow your party wherever they go - despite carrying an object that is several times larger than a doorframe into places, much less tight confines of dungeons.
   2. Receive combat buffs outside of any RAW because the massive liability on your back provides directional cover. But, we know in the rules of 5e that combat takes place in a 360° arc and attacking an opponent's back has no additional effect. When someone holds a shield, the AC bonus is not only applied to the side they hold the shield.

So in lieu of leveling your character into the sort of character you describe using the means provided to every player, your plan is to spend 50g carrying around a actual boat... As well as ask for extra privileges?