I recently took delivery of some Desser Monster 600-6.0 6 plys and installed them yesterday. What a difference they make and can't believe I never had a puncture with the AirTrac 4 plys as there didn't seem to be too much between the tarmac and the tube when compared to the "monsters".
Have also gone with the consensus and fitted an Aero Classic 400-6 6ply to the nose wheel.
Thanks to all for the helpful advice on tire selection.
We had quite a hassle initially trying to fit the "monsters" without pinching the tubes in the Matco split rims until I found a post on another forum (from quite a while back) by Roger Lee where he suggested using some woodworking clamps, which subsequently made the task very straightforward.
Perhaps Roger might like to re-post that information here as it may save others a lot of anguish.
Dave