Your health regenerates 1 point every 5 minutes, so 12 health per hour. On average, when you are attacked, you will loose between 15-26 health when attacked.

So, the maximum you can be attacked is 1 per hour.

"Army Camping" is when you camp but defend yourself from attacks

"Naked Camping" is where you camp with no units that cost you upkeep which usually means you have no defence against attacks

So, if you have any intention of "defending" a camping position and you spend more than $50,000 per hour "defending", you are already loosing money as compared to just allowing them to attack you.

The same applies in the game generally, whats the point in defending. Even if you earn less than these, the amount is roughly 20% of what is left out, upto the above maximums, so you can't loose.

There is no point defending a camping position unless you worry about your attack win/loose ratio