I know you briefly explained the bottom field, but can you explain the process in a bit more detail.
Well mate its like Dave said really just hold out until the end but a few tips I can give are;
When you start doing the piggybacks your near the end, make sure you do what they so 10 press ups not 9 they DO count you, aim to be first on the sprints, and the last one, smile while your doing it even if your dying inside smile, it will show that cheerfulness.
But Bottomfield is basically, you practice on the ropes, do as they say or you'll be there all day!!! Then you go round the assault course learning how to do it properly, then you do your timed run (easy to do in 5 minutes mate) then you sip your water and start the determination tests it lasts about 25 minutes and your just sprinting round the obstcles come back do press ups, sit ups whatever then sprint some more
