For many years most Airstreams built did not have spare tires because they could run on three wheels in case of a flat tire. They still can today, you just max the pressure in the remianing tire and keep your speed down to 50 MPH. Generally though you do not have to run very far to get a replacement tire.
The Michelin's are not run flats but they almost never have a flat. In all the traveling I have done I have never had a flat with a Michelin and I can only think of a couple of customers that have. The more common trailer tire problem of belt separation never occurs with the Michelins. In old days when a spare was an option we would suggest to customers spend the money on a michelin upgrade and you won't need the spare.
There is still weight on the tongue it is just being transfered to various axles instead of all going on the rear axle of the tow vehicle. It would be even more than 700 on the rear axle since you would be leveraging behind it. So without the weight distribuion this combination would be something like -300 on the front, 1000 rear and the trailer would stay even.
Hi Robert I weigh quite a number of combinations so I do not keep all the tickets.
"One test is worth a thousand expert opinions."
Tex Johnston, Boeing 707 test pilot