Taking 40 high school kids (+3 staff members) to Thetford for the day in July.

Kids are on the coach, bikes travel seperate.

Could I fit 43 mountain bikes in a long wheel base transit or does that need a Luton Van?

If the price is the same (or near), go Luton – you can never have too much space.

I'm not too sure 43 bikes will fit in a Luton van, if you pile 'em high and don't worry about scratches and scrapes then you might be ok … I'd certainly be wanting a trial run.

might be able to pack them in the coach too?

there was a similar post last week relating to a charity event (think was in post title along with transit) and quite a few people who seemed from experience to know exactly what would fit and how

Work did the london 2 brighton a while back and used a coach + a luton.

IIRC you can't get that many in, but I may be wrong (and you may be able to pack them more creatively that us!), if possible I'd try and get some sort of test run, or go for the Luton if its not too expensive just to be safe!

here it is
http://www.singletrackworld.com/forum/topic/help-how-many-bikes-will-i-fit-in-a-transit

I would rather swop and put the bikes in the coach so as not to scratch them