Hey mate first of make sure you don't train 1xp of defence the following quests are essential and give enough xp!
The Fremennik Trials -2.8k Defence xp
Dragon Slayer -18.6k Defence xp
Monkey Madness -20k Defence xp but choose the option which does not focus on defence
Nature Spirit -2k defence xp - need this quest for barrow gloves
Holy Grail -15.3k Defence xp
Heroes Quest -3,075 Def Xp
Even if you fall short of 45 don't hand train it for now, trust me thell be some quests that pop up later that youll need this way you don't have to go over 45 defence.
I also suggest you look into Turmoil as well and train as if one day you would like to get turmoil..
Some essential items any zerker needs
-Barrows Gloves (RFD)
-Vengance (94 Magic)
- Magic Book (zammy)
- Proselyte Armour
-Fighter Torso
-Fire Cape
- Rune defender
-Full void
Ultimatly you want stats like
Attack: 75-99
Defence:40-45
Strength:99
HP: 99
Range:99
Mage:99
Prayer:44-95 (completly up to you)
Anyway goodluck and feel free to pm me for any questions about zerkers/rune pures