Yes a split charge relay is very easy to fit, and as you suggest, a dual sensing voltage sensitive relay (VSR) is the best solution for you if you are on a budget, as no alternator/ignition connections are required. I would advise a kit, but a decent one. For mine I used:
http://www.12voltplanet.co.uk/split-cha ... asure.html I'm sure other members of this forum will agree that this is a well put together package. I can't rate 12V Planet highly enough. Apart from a great product they were very helpful (and no I don't work for them and am not affiliated in any way - just a happy camper!) Fitting the kit is nothing for you to worry about, just connect the VSR positives to each battery, and the VSR and leisure battery earths.
Above I say 'on a budget', as there is a much better (and just as easy) option, but it is a LOT more expensive. This is 'battery to battery charger' (B2B).
http://www.12voltplanet.co.uk/sterling- ... v-30a.html Unlike a VSR (which is just a trickle charge), a B2B is a proper multi-stage leisure battery charger, that uses a stepped charging protocol to charge your battery much more quickly, more fully (approx 100% compared to 80%), and more safely (your battery will last much longer). It's the same thing as a mains leisure battery charger but it runs off your starter battery. It also has all the split charging and safety features built in. Just plug and play, exactly as for a VSR.
If your van has a smart alternator (variable output) and you don't want an ignition-driven relay switch, the a B2B is the only option, as a VSR won't work with a smart alternator (as the alternator output is too low at times). A B2B on the other hand uses advanced circuitry to 'trick' a smart alternator into delivering max output as required. However, your Y reg van almost certainly won't have a smart alternator.
I went for a B2B purely because I have a smart alternator, and like you didn't want to connect to the ignition circuit. But I'm soooo glad I did. The thing works like a dream and charges my leisure battery so quickly that with even a small amount of driving each day I never have to use a mains battery charger at all!
Hope that helps - HT.