Realistically you will not get what you are asking about. The only service that is actually cable speed is 4g. The problem with 4g is that it is only available near/in large cities. It will drop down to 3g or even much slower when you are between cities. Your requirement to have it available when driving may be a deal breaker too. Satellite will provide your needed speed but only works when stationary. Other connections such as park wi-fi and cellular 3g or 4g will bog down with the number of users. Try going to Arizona in the winter and see how fast their networks are! Data limits are just a function of how much you want to pay. If I were you, I would figure out how to do your work only when parked. Another thought is that some parks will allow you to get cable Internet at your site if you stay there all winter. That doesn't help however when you are moving around every week or so.
Full timers roaming the good old US of A
2007 Itasca Suncruiser 38J
2015 Jeep Cherokee Trailhawk