Hi Fettsbabe,
I am concerned because it sounds as though they are growing pot in the RV. A friend of mine had a similar setup years ago. If it were meth, you would smell the chemicals and it would not be necessary to constantly have a light on inside.
Is the light eminating from the RV of an orange tint? If so, they are using high pressure sodium bulbs to grow the plants. I'm not sure why they'd need propane, it might be unrelated, but the hose is probably for the sake of easy watering (in the case of soil) or for a resevoir (in the case of hydroponics). Someone mentioned this earlier, but they were wrong in assuming that one can use the municipal water pressure in place of a water pump. The fan you hear is for air exchange to bring in fresh air rich in co2 and to expel air whose co2 has been used in photosynthesis.
If they are indeed growing cannabis, the lights would be on 24/7 initially, then they would switch to a 12 hour on, 12 hour off cycle for the flowering period (when the buds are produced).
Now, this brings me to the reason why I registered. You state that you have kids and do not want some druggy neighbor living next door. This is completely understandable. However, I feel that you are taking a bit of voyeuristic pleasure in spying on them and posting this thread.
If you genuinely fear for the safety of your children, then I would recommend simply talking with them. If you have the bravado to spy and take pictures, and intiate this thread for that matter, then you should have enough courage to talk to them face to face about your concerns. They are not harming you, so it would be bad karma to get them in trouble with the law without first addressing your concerns to them directly.
Go over there tomorrow and tell them that you think they are up to something and that you fear for your childrens' safety. If they are respectable people, which I have no reason to doubt, then they will appreciate your concerns and either stop what they are doing or let you inside the trailer to show you that nothing illegal is going on. Problem solved.
If neither of these occurs, then warn them that you will call the cops. This is fair warning for them to stop what they are doing.... if you were in their shoes, you would appreciate this courtesy.
By the way, I am a cannabis grower and I can assure you that a few plants pose no danger to your children. Any sane grower locks their growroom and most potheads are not dangerous people. However, this will not dissuade you as your mind seems to be made up.
I think the humane thing to do is go over there and talk with them. They are your neighbor's for crying out loud!! Get to know them, or at least give them warning that if they don't do something, they may lose their freedom for an extended period of time. In our hobby, nosy neighbors are a constant threat. And, sadly, most of this is due to ignorance....
Regards,
A Fellow American