Tracker, I am in the midst of building a drawer system for my BT50. In front of that I have a dedicated box so to speak that contains a 53 litre water tank, pressure pump and 130AH battery. As Hem has done, the weight of this is supported by the base, which is 12mm ply, this spreads the load across the whole floor area. Where it extends past the corrugations in the floor on the sides, I have packed that area up so it is also fully supported and not floating in mid air.