While repairing the truck for the neighbor on the surface sounds like a really magnanimous gesture, I'm not so sure it is the best solution. To begin with it assumes the OP is in a position to make such an offer. On top of that there is much speculation as to what it would cost to make the repairs. That is not something that can be estimated unless one knows exactly what repairs are needed and from the limited information here that is not something one can ascertain. We also do not know what mechanical ability the OP may or may not possess. Additional labor costs could add up very quickly. Even assuming the OP possesses the ability we don't know what tools he has available. Remember he is in a campground or rv park so certain types of repairs may not be easily done in that situation. The neighbor may also not be receptive to such an offer.
As I see it the OP has a few other options. What works best in this situation is something he is going to have to decide.
He can complain to management and ask them to either intercede or allow him to move to another site (assuming there is one that would be far enough away).
Packing up and moving to an entirely new park.
Getting some ear plugs and just ignoring it.
Try establishing enough of a rapport with the neighbor to discuss the problem and hopefully agree upon a solution. This is probably what I would first try however not knowing the people involved it is impossible to say.
Just learn to live with it.
Resort to other more retaliatory type measures which run the risk of inciting the situation.
Someone alluded to a meth lab being nearby. I know based on what was posted it is baffling why he/she came to this conclusion. However the OP has stated that the vehicle leaks gas and on "some" days the smell is overwhelming. He has also said that the husband or at least man living there stays in all day with windows and doors closed. So question is does truck actually leak gas? If it is leaking enough to create the smell described there would most likely be some sign of it. Is that smell really gas? A meth lab can give off a very strong chemical odor, not really a gasoline odor. If you have ever been near one you would understand. Just saying the possibility does exist. If, and that is a big IF, that is the case it is not something you want to be next to or people you want to interact with.
