anyone biked, camped there out of summer season ?
Yes.., When? Season is longer than France.
where do you want to camp? and how? Often seen a few camper vans parked up on the far side of the W hotel. There aren't really any campsites in the resort or village. Some down in the valley though only a cable car journey away.
Fairly long season there, main lifts run till end of October, ie up from Les Chables and the Medran. This serves a decent portion of Enduro and Bike Park (less top two shortish easy red runs). Also Savoleyre lift only runs July and Aug. Never really seen any Camper Vans and anyway staying down the hill is good for biking as enduro trails finish in the valley. Other thing I would say is bike park is relatively tough with 1 blue and main reds are quite tricky.
I love it there, 2016 is first year in a while I didn't go there for at least a long w/end. Bike Verbier if you want to make the most of the area, guides and uplifts and lots of riding away from main Verbier bowl. Relatively pricey but includes food etc.
If you want to do a September trip you can catch the last few days of Chamonix and then head over to Verbier/Les Chables an hour away. You can check the Post Bus too as that will take you up in Bruson and also to Verbier village once the left stops running around 1700.