mate,its like couples like to be could be the girl using a sex aid,or shagging her couples like full on,extreme anal fisting,strap-ons,multi-partner gangbangs with cum-facials,scat,g-spot ejaculation,dp and spitroasting to finish...at the venue we use,i'd say some kind of involvement was more common,but what difference does that make?...find a level you are both happy with,that will be more than satisfactory.
norwichlad- your gf sounds just like me- maybe we should have a 3some ;o)
yeah mate - i am new to this too - i went to a trowse location (where do others go by the way?) and on my first night i got to help a guy use a dildo on his partner, lean in the car (was not allowed any further inside - but then there aint much room!) and suck her tits, and then she sucked me off too - as well as just the lovely sight of her sucking and wanking and riding him!
so its up to you what/how much you do...
if you do go dogging in the near future gimme a shout - we are both new to this andm ight be a good start? of course you could pick any chap ;-)
loz