Kyle
Tip up in a suit but take some "smart casual" stuff with you too (ie shirts with a collar, and other trousers). The suit will set a good impression to begin with and then if you change for the subsequent days you will find it more appropriate and more comfortable whilst still being acceptable around the mess etc.
Assuming you'll be staying in the Officer's Mess, give the mess a call (get Boulmer's number and ask MOD (Mis-)Directory for the Officer's Mess reception) and find out the mess dress rules. Being an Army mess, I'd imagine you would have to wear at least a collar and trousers in and around the public rooms. When all said and done, don't fret too much about it and if in doubt ask someone. They may be FCs, but some of them will still be able to string a sentence together.
Ask lots of questions, appear interested, ask lots of questions and enjoy yourself - that way you'll get the most from it.
Shemy
Don't be such a patronising little arse. I'ts not so long since you were posting here asking bone questions.