I'm assuming I can NOT use an RV park with a 50 amp service.
Not true. There are adapter for the various combinations of availale power outlets and trailer plugs. Parks that have only 50A outlets (the one I'm in now is an example) usually have 50A-->30A adapters to loan out, but you could buy one of your own for around $25. You should also get a 15A-->30A adapter (under $10) so you can plug into a 15 or 20A (standard household) outlet.
How do I make sure the service is 30 amp?
The plugs and therefore the outlets are different configurations which you will quickly learn to recognise. A 50A plug has 4 blades and the outlet has 4 matching slots. A 30A oulet matches the one on your rig, 3 large blades on the plug in a triangular pattern. 15/20A outlets look like and are standard residential power outlets. Here's a link to a page that illustrates and explains
RV power plugs.
And there must be an inexpensive polarity tester, correct?
Sure - you can buy one for $4-$10 at most any Home Depot, Lowes, Radio Shack or probably even Walmarts. They plug into a standard household outlet and show polarity via three indicator lights. It can be used in combination with a 15A-->30A adapter to test a 30A outlet as well.
Here is an example of one.
Campground power outlet problems can happen, but aren't anywhere as near prevalent as all the war stories and magazine articles would have you believe.
Do all MH's come equipped w converters? Do the converters convert 30/50 amp to 110 for interior use?
Yes they all have converters or the equivalent, but that is not what supplies interior AC power. That comes directly from the shore power plug or a generator. Optionally, some motorhomes have inverters, which can convert battery DC power to 110VAC. A converter supplies 12VDC power from shore power (110/120VAC) and charges batteries. An inverter may include te converter/charger function or may be an inverter only.
And once I'm hooked up to shore power, I can run everything in the MH - including heat/AC - and live large - right?
Large? Probably not with only a 30A supply. 30A gives you a max of 3600 wats of power and usually a bit less, around 3300. You will soon learn to count watts (power consumption) of the major appliances you use, becasue you will trip circuit breakers if you don't. You can generally run one a/c unit (not two) because an a/c consumes 1200-1500 watts (depending on make and model) while the compressor is running. If the microwave is running (consumes 1000-1200 watts) you may not be able to run the a/c at the same time. Coffee pot is around 1000 wats when perking, ditto for toasters. If your water heater is onl electric rather than propane, it will consume 500-800 watts while actually heating and you can't predict when it will be on and when it is not (it is thermostatically controlled). If you use a electric space heater, it will use 1000W-1500W