If I were advising a client..............I would make really really sure there was ample business purpose........and that it was obvious enough to me that I would feel comfortable about defending it.   

"Disguised family vacations"---------- I wouldn't even try it.  Too many penalties for doing blatant things anymore.

That much travel expense sticks out in a Sch C or F like a sore hicky................that much money in those captions is just not "normal", and upsets the "picture" that a tax return should paint.

On things of that nature, I take the position that if a materially-significant item is questionable at all, if my testes tighten when I see/hear about it, then the item needs to be highlighted in the return, ie made an issue of.........so that the documents are known to be tight (who in their right mind would include a bunch of documents with a tax return that they were not sure of??), and the related tax law is discussed...openly.....in the return..................kind of like when a coach moved me to a defensive tackle position for a game 'cause the opponent ran the single wing (of all friggin' things)--------his comment------Boy, they're gonna run through you nearly every play, tell you when they're coming, and dare you to do anything about it!   Makes everyone honest!

Point--------if the item cannot stand the test of being highlighted---------don't include it.

We do work for some Beverly Hills doctors...........really uptown operation.........go all over the world lecturing, etc etc........

Their returns run about 1-2 inches thick due to the documentation we pile in, especially on the overseas travel.........copies of the lecture programs, topics, etc etc................just to allow the IRS to ask and answer the questions they might have while staying at the service center instead of feeling the need to do a home visit.

But, note, the items are obviously highlighted, just due to the attachment of the documents.......even if the amounts of moneys "fit" in the return.

Check section 274.............and especially the regs related thereto.  Special rules kick in when crossing an ocean.

I think IRS has a publication or two directly on point-----------go to IRS.com     publications     and browse their topics list.