Warner Glen is a DEC managed campsite with two camping areas to suit individuals and groups.
It is situated near the juntion of Blackwood River & Chapman Brook.

Directions:
It is 15kms from Karridale, off Warner Glen Road.
From Margaret River, drive south along Bussell Highway, turn left onto Warner Glen Road. 
From Karridale, drive east along Brockman Highway and turn left into Warner Glen Road
.
The lower loop near the river is suitable for small vans and individual camp sites.
The group loop can cater for large caravans, or multiple tents.
I don't recall any drive through sites.

Facilities:
The group loop has an undercover camp kitchen with gas hotplates (no fridge).
Central long drop toilets.
Fire rings and picnic tables at each site, however fire restrictions do apply during November-April
Some firewood may be available but will probably freshly cut mill ends - too green to be useful.

There may be camp hosts in situ during school holidays.
Canoe launching facility nearby.

No generators are permitted.
Dogs allowed - on leash at all times. 

Costs:
DEC camping fees , No park entry fee applies
Adults [16+]  $7/night;
Concession $5/night, companion card free;
Children [5-15] $2/night.
Children under 5 are free

Opinion:   
We enjoyed a very relaxing 6 night stay when it was not school holiday period.  Apparently, it can be very busy at certain times of the year. 

First come-first served means there is no guarantee, however Contos, Alexandra Bridge and Sues Bridge are not far away if  need arises.