I used a hard shell bike box, the bike has survived (pipe insulation and copious amounts of bubble wrap) but the box has got damaged a few times. This year for an easier life, I'm sending my bike to Rimini fully assembled over land with Tri-camp. (Pain in the ass assembling and packing the bike) one less thing to worry about. FYI race force were brilliant in Majorca last year (we didn't use them but they were happy for us to get our bikes checked out ad hoc if we needed to) there support for the Brits, whilst we were training was outstanding.
I did challenge Pageura half(Majorca) last October, the cycling in Majorca is cracking, a bit of everything. The run was quite hilly, which was tough on tired legs....oh and bonus, the weather was gorgeous! I'm assuming the ironman will be just as good! (Could see me joining you, I was going to enter ironman Wales!)
Ironman Holland could also be a good race, I used to live quite close to that area! Cheap to get to and loads of campsites ????