For those of you in colder climes who race/have raced in the hotter parts of the world, what advice can you give me?

I live and train in London and have IM Nice coming up in a couple of months. My training has been in cold, damp wet British weather and it doesn't look like it's getting better any time soon.

I'm looking for advice on clothing, hydration, acclimatisation......

Should I be racing in a full sleeve light coloured top to reflect the sun and hold water or would it just keep me more insulated and a smarter plan to be to go as skimpy as I can? I've a long (full) sleeve white tri top on the way so keen to give this a go if the weather turns nice in London at any point in the next few months. I'm also planning on wearing a light coloured mesh "trucker" style hat to keep the sun off my head, allow airflow and to have a good way to keep ice on my head.

I'm planning on racing with tailwind as my primary source of nutrition as I found it annoying having to carry pockets and a bento full of chopped up clif bars. I'm currently training with this and it's going really well.

My gym has a sauna. Is there any benefit in me spending time in there every day to get used to heat? Due to work and family commitments, I'm only going to be able to get down there on the Thursday/Friday before the race (Sunday) so there won't be much opportunity to do any real acclimatisation.

Any other tips would be greatly appreciated.