Welcome to RIBnet Rumrunner,
As I don't know exactly what you have tried - I'll tell you what I'd do. Firstly, deflation over 48 hours is a decent leak, if you inflate the tubes to working pressure, there will be an audible hiss somewhere but possibly not enough to use for locating it (ask a child to listen - they have good upper range hearing). So pump the tubes up until your fist bounces off them - you need a mixture of washing up liquid and water - make it strong 4:1 maybe and spray it on the open areas if you wish but PAINT it on with a brush over the tapes, seams and valves. Open the valve cover before you do this. Pay attention to cone ends and the areas where the tubes meet the hull, both inside and outside. I would do the adjacent tube too as air might be passing along inside the tube/hull contact area and escaping from below the next section up - hope not though!
Pay particular attention to the areas that would be under water.
Until you know where the leak is, I wouldn't start looking for sealers etc., unless the tubes are old and knackered.