Satellite Internet and Television
Not all cable installations will offer internet, and if they do, you will probably need to use their ISP. Not something you can find reliably, and may not be optimally usable.
Unfortunately, there is no one solution to both uses. For TV, your choices are: Built in antenna (directional or omnidirectional), cable from the park (great if they have it but not all do) and satellite (Dish or DirecTV). For internet, your choices are: Telephone line (not all places have it and those that do tend to charge extra), wi-fi (great if they have it and it is set up right), cable (somewhat rare), wireless (cell phone or other), or satellite (Starband and Directway, I think are the names).
As far as the built in antenna is concerned, I had the crank up, rotatable (directional) antenna on my old trailer, and it always did an adequate job. A couple of things to check: make sure that it has a working amplifier and that it is turned on. Makes a big difference in the signal. Also, check your TV; many have a cable setting and an antenna setting, and if it is set to cable, the antenna won't work very well if at all. Finally, make sure you have it pointing in the correct direction; these are highly directional.
The motorhome has the static, round, omnidirectional antennal. I'm not thrilled with its performance so far, but again, turning on the amplifier moves it from unusable to possibly bearable. Since chopping a hole in the roof to put in a better antenna is not desirable, I'm looking into activating the already installed satellite dish.
Satellite seems the optimal way to go. If you have this service at your house, you can usually add the RV 'for free' if the antenna is already installed. Otherwise, make sure the company has a 'suspend service' option so you don't have to pay for it while the RV is not being used. Satellite service tends not to provide 'local stations' except at your house in some areas, so you might want to spend the extra to get either the east coast or the west coast networks (ABC, CBS, FOX, NBC, PBS, UPN and WB). Or you could just try to use the antenna for local stations.
Built in dishes can be had in manual, auto seek, and in motion, in accending order of cost and ease of use. Note that trees or most anything else will block the satallite signal, so if your RV does not have a built in dish (or even if it does), you may want to have a manually set up dish on a tripod, and a roll of antenna wire.
If you use your cell phone for internet, be advised that they charge by the minute, so make sure you only compute during your 'free nights and weekends' time and within your 'no roaming fee or long distance' area. There is also at least one wireless service out there which charges by 'data transferred' rather than by minutes used.
Mobile satellite internet is still growing. One company does not seem to support mobile use (although many people do it) and the other will certify you as an installer so you can legally set up your dish anywhere you happen to be. Also, one of the companies offers the option to add a satellite TV LNB to their dish, but the service still needs to be contracted with the TV company (one dish, but 2 bills and 2 companies to deal with).