Just to update this - for the limited use I cannot justify the £125 on a Bravo so went to our local camping superstore and bought these (Gelert Hurricane 3 12v and 240v electric pump (£13.99), generic DA 4 litre stirrup pump (£6.99) and the best bit - 2 metres of really heavy duty convuluted waste pipe).
The stirrup pump is surprisingly well made inside (exactly the same as the marine branded ones I reckon but at 1/3 the cost) - opened it up to fully grease it. I wanted an electric pump that did 12v and 240v for all the times it is inflated in the garage/back for cleaning etc. This one:
GELERT HURRICANE 3 240V/12V ELECTRIC AIRBED PUMP CAMP: Amazon.co.uk: Sports & Leisure
Weak point on these things is the fittings and hose - replacing with the HD hose makes a big difference to ease of use and durability.
With a combination of odd pieces of thick PVC pipe and adaptors both pumps are usable at the same time and fit either valve on the Zodiac.
How does it work? For the money, fantastic. The electric pump will inflate each of the chambers to low pressure in around 1 min each. A further minute or so of hard effort with the stirrup pump finishes each of them off including the floor to high pressure - while the electric pump does one you can stirrup pump another. Not quite as easy or quick as the Bravo but half the time it took me with a foot pump.