but I'm interested in seeing what some people reply with coz I've wanted to do the exact same thing in my tinny, good luck mate

 If you've got a 4WD launch from Quindalup otherwise Old Dunsborough is your go. Both have jetties.

On a clear day you can see the big sand patches in the weed bed so just drop into those for KGW and it's always worth having a herring on a squid spike on a float too.

 I used to go out from Port Geographe marina, very good launching facilities there. KGs were my specialty. Once I cleared the mouth of the marina, I'd track off slightly to the right. Once you get out about 3k, you should be out in front of Wonnerup and in around 40ft of water, look for the sand patches between the weed like JF has said. Don't anchor because if you don't get anything in your first few casts, or the trumpeters are there, move on. Sometimes you might need to move a dozen times, but if the KGs are about, it's worth it. Fish can get up to the 45cm mark but average 38-40cm. Fish this size don't hang in big groups, your likely to only catch 2 or 3 from each spot you find them and if they are there, you'll pick them up fairly quickly. Best bait is a combination of squid and prawn on a wide gape hook, about size 1/0 or 2/0. These fish will hook themselves with that set up. Fish reasonably light and they will fight you all the way to the bucket. 

 ....use the tentacles for bait. Paternoster rig, and for hooks I'm a bit different to Dale; beak style in size 1.

Apart from that, as above. Keep on the drift, dropping your gear into the sand holes. My experience has been in the siesta park area, about halfway between Busso and Dunsborough, and in water 4-5m deep.

If the missus is keen for KGs, she probably wouldn't mind yellowfin whiting either. No boat required, simply wade out onto the flats all along there and flick little poppers/stickbaits around, same gear/technique as for Swan river/Peel and Bunbury estuary systems.

 Some big hezza hang out in the weed bank adjacent to the old Dunborough boat ramp too and they love a shallow diving minnow

 As the guys have said above. You will increase your catch if you take the time to catch some fresh squid, definately the best bait for them.

Also daybreak is when they are on the chew the most, early this time of year but worth it. 

 Thanks for the insight people - where would the best boat ramp to launch a little tinny from and get into the action as quick as possible ?

Cheers  

Old Dunsborough is perfect for a tinny. Used to stay in a caravan park right near there and we just headed out in tinnys straight out from the Old Dunsborough bay and usually got into a feed of KGW. The 4 Mile reef wraps around the coast along that stretch so there's a few inconsistent lumps to be found not too far out. Found some nice lumps only 0.5nm off Meelup in the 16m depth during the demersal ban.