After implementing @jack suggestion, i  have an error which. The view can no-longer find the already defined model fields. 

Below is the error.

Note: I have a model file which is inheriting the same model as the view and the 'missing' field is already defined there. 

Advanced apologies if am asking the obvious but apparently, i can't seem to figure this one out

Thanks

 <?xml version="1.0" encoding="UTF-8"?>

<odoo>
    <data>

        <record id="picking_orders_additions" model="ir.ui.view">
            <field name="name">liroi_fields.picking_orders_additions</field>
            <field name="model">stock.picking</field>
            <field name="inherit_id" ref="stock.view_picking_form"/>
            <field name="arch" type="xml">


                <xpath expr="//field[@name='move_ids_without_package']/tree[1]" position="inside">
                         <field name="gross_weight"/>

                </xpath>

            </field>


        </record>

    </data>
</odoo>



# -*- coding: utf-8 -*-

from odoo import models, fields


class PickingOrdersFields(models.Model):
    _inherit = 'stock.picking'

    gross_weight = fields.Float(
        string='Gross Weight',
        # related='delivery_id.weight',
    )
    tare_weight = fields.Float(
        string='Tare Weight',
        # related='delivery_id.weight',
    )
    moisture_cont = fields.Float(
        string='Moisture Content',
        # related='delivery_id.weight',
    )

Hello,

There are quite a few things wrong here, but I will try and help you best I can. Your first attempt (commented) looks promising. We all start somewhere.

Below is an example where you would have a One2many with a student model and you would like to add the last_name field to the tree view (it only has the first_name defined so far). 

If the form view is displayed as something like:

<field name="student_id"> 
    <tree>
        <field name="first_name"/>
    </tree>
</field>

You would inheirt the view like you have done and then add the field using the xpath. The expression would be:

<xpath expr="//field[@name='student_id']/tree[1]" position="inside">
    <field name="last_name"/>
</xpath>

This has added the field last_name from the Student model into the One2many.

I hope this helps if you need anything clarifying feel free to email/comment.

BTW I believe the notepad doesn't really matter as long as you start with //field_name

Thanks,