batterys in a jayco hawk

I have a jayco swan out back 84 model , i have put my two deep cycle batteries
as close to the centre as posible , in a cabinet that is on the right just as you walk in the door . Just happens to be right in front of the axles , this might work for you as your layout may be different. Good luck

Most people put them under the couch, which I think runs in front of the main bed.

As for............

"i was told thay should not be placed rear of the axel(as vibration will wreck them)"

I don't think it's viabration that dictates you don't put them rear of the axle, it's more likely to be a balance thing.

Jayco campers are balanced to have around 120KG on the towball. Puting heavy objects rear of the axle upsets this balance, and if you have ever towed a trailer that "wags the dog" you won't want to do it again. What happens is, you get steered all over the road by your trailer, and at 100 klm it's quite scary.

G'day emgirl, On our Jayco Dove we placed our battery in the cupboard, below the sink

We have a 2004 Hawk ob with a deep cycle sla battery located in the compartment behind the setec power unit (the obvious place as you suggested). To prevent any movement, the battery has been fastened securely to the floor using some battery clamps (purchased from BatteryWorld). Wiring was straightforward as close to setec unit where wires connect. An isolation switch and voltmeter (purchased from Jaycar) were installed on sidewall of battery compartment which is also accessible from external storage door - that enables convenient isolation of battery during storage and monitoring voltage during periods of use.

Travelled well over 10,000km (incl several 1000km offroad) and no problems yet...