I use the big Peak Design slide on my Mamiya press, Bronica sq-am and -ai so I can easily switch the strap and feel sure it will hold the weight and only need the one strap. Also use a PD leash between a Canon A-1 AE-1 and couple of other 35mm's.
BUT Having recently bought a guitar I have realised just how cheap these could be made with a guitar strap. With a little ingenuity, some Kevlar cord and a carabiner type clip you could have great strap for £10.